CBS News via AFP - Getty Images

This image obtained April 19 courtesy CBS News shows Dzhokhar Tsarnaev, a suspect in the Boston Marathon bombing who was captured hiding in a boat in a Boston suburb.

Bleeding and hunted by police, Dzhokhar Tsarnaev scrawled a note inside the hull of the boat where he was hiding saying that the Boston Marathon bombings were retaliation for American action against Muslims, sources told NBC News on Thursday.

In the note, Tsarnaev, the lone surviving suspect in the marathon attack, said many of the things he told investigators from his hospital bed days later, after his capture, the sources said.

The note was first reported by CBS News.

Tsarnaev was discovered hiding in the boat, in suburban Watertown, Mass., on April 19 after a daylong manhunt that paralyzed Boston and its surroundings. He had been wounded in a firefight with police.

Tsarnaev, 19, is in a federal prison hospital in Massachusetts and has been charged with using a weapon of mass destruction. He could face the death penalty. His older brother, Tamerlan, was killed in the firefight.

Three people were killed and 264 injured when two bombs exploded near the marathon finish line April 15.

Dzhokhar Tsarnaev told investigators in the days after his capture that the brothers acted alone and were defending Islam after the American-led wars in Iraq and Afghanistan, U.S. officials have told NBC News.

Investigators are also focusing on a six-month trip to Russia that Tamerlan Tsarnaev made last year, looking for clues to his radicalization. He was buried last week at a Muslim cemetery in Virginia after cemeteries in Massachusetts refused the body.

This story was originally published on Thu May 16, 2013 8:02 AM EDT

John Makely / NBC News

Fernando Colon was accused by Ariel Castro in 2004 of sexually assaulting the latter's daughters, Emily and Arlene, who also were his stepdaughters. He was initially charged with 28 counts, including rape and kidnapping, but was found guilty of five lesser offenses.

Nearly a decade before being charged with kidnapping, raping and torturing three Cleveland women, Ariel Castro was himself the accuser in a sexual assault case involving his daughters. The accusations, which resulted in the conviction of his ex-wife’s second husband, now offer a new window into Castro’s tangled family relationships. 

The case against Fernando Colon also raises questions about whether FBI agents squandered an opportunity to question Castro about the disappearance of two of the women in the months after their abductions.

John Gress / Reuters

Ariel Castro appears in court Thursday in Cleveland.

Castro made the accusations against Colon, 39, in July 2004, shortly after 14-year-old Georgina “Gina” DeJesus vanished on her way home from the west Cleveland middle school she attended. 

Colon, the husband of Ariel Castro’s ex-common-law wife, Grimilda “Nilda” Figueroa, says he told two FBI agents nine years ago to investigate Castro in connection with the disappearances of Amanda Berry and DeJesus, but that the agents seemed uninterested in his tip.

Castro has now been charged with four counts of kidnapping and three counts of rape for allegedly abducting DeJesus, Berry and Michelle Knight, and was arraigned on Thursday.

When DeJesus, a seventh-grader, disappeared on April 2, 2004, the FBI had reason to question Fernando Colon. Colon, was the stepfather of 13-year-old Arlene Castro, Ariel Castro’s daughter, who was DeJesus’ self-described best friend and had been with her right before she vanished. He also was the last adult known to have seen DeJesus before her disappearance. 

According to Chris Giannini, a private investigator who at the time was Colon’s boss, when school let out that day, Arlene Castro and DeJesus walked to Westown Square, the nearby shopping center where Colon worked as a security officer. Arlene asked Colon if Gina could come over and spend the night. 

When Colon said” no,” according to Giannini, the girls tried to get around Fernando “by checking with mom” via payphone. He said the girls got a second “no” from Figueroa.   

'The last one to see Gina'
After  Gina DeJesus disappeared, Arlene Castro told investigators that she and her friend went their separate ways when their sleepover was nixed. But according to a Cleveland police report issued Wednesday, Gina DeJesus has added a new detail. She says that before they separated, they also talked to Ariel Castro. After the girls split up, DeJesus now says, Ariel Castro returned and offered her a ride, which she accepted.

Soon after the disappearance, FBI agents contacted Giannini and said they wanted to question Colon “because he was the last one to see Gina,” according to Giannini. They searched the patrol car that Colon used to cruise the Westown parking lot to make sure Gina had not been in the car. According to Colon, FBI Agent Phil Torsney and another agent whose name he doesn’t recall then conducted a polygraph. 

“I guess I passed the polygraph,” recalled Colon. Having taken courses in policing, Colon said he understood why he had been questioned, but realized that there was someone else the FBI agents should contact. 

John Makely / Courtesy of Fernando Colon

Fernando Colon keeps this photo of Grimilda "Nilda" Figueroa in his Cleveland apartment.

According to Colon, Castro, who had not spent much time with the girls since splitting from their mother in 1995, and had contributed little to their financial support, had recently started spending more time with  them, driving them places and buying them cellphones. Colon said he told the agents that Castro also might have been acquainted with two of the missing girls -- in addition to Arlene’s close friendship with DeJesus, his older daughter, Emily, was friends with Amanda Berry, who had disappeared nearly a year earlier. 

“I said that if you’re talking to me because of my stepdaughters you should really be talking to Ariel Castro. He has more chance and opportunity than I do,” said Colon. “These girls are best friends with his daughters. (The agents) told me, ‘Well, we have to deal with you. Whatever arises in the case, we’ll take care of that.’” Colon does not know if they ever followed up and questioned Castro. 

Agent Torsney, who is now retired from the FBI and living in another state, did not immediately respond to a request for comment. At a press conference Wednesday, FBI Special Agent Stephen Anthony took issue with Colon’s version of events, telling reporters that his agency had "scrubbed" its records on  the case and had found no mention of Colon referring to Castro, and had “no reason to believe” he’d made the statement. 

Colon says he heard nothing more from law enforcement about the DeJesus case after the polygraph. Several months later, however, Colon found himself under investigation for a different crime. Ariel Castro and his daughters Emily, 16, and Arlene, 13, alleged that Colon had molested both girls between 1996 and 2001. 

Payback seen behind accusation
Colon maintains his innocence, and told NBC News that he thinks Ariel Castro made the accusations as a way of fulfilling a threat he’d made back in 1995, when his wife left him for Colon.

Grimilda Figueroa and Colon met when Colon was working at a local hospital, and Figueroa came in with injuries that she said were the result of abuse by Castro. She had accused Castro of domestic violence in 1993, but a grand jury declined to indict him. 

After she’d come to the hospital a few times, Colon said he offered her a way out of her relationship with Castro. “(Castro) had so much control over her,” Colon said. “He had her so wrapped up she had nobody to talk to. She told me his windows were tinted so nobody could see in and there were padlocks on the doors.  . .  I said, ‘If you were offered help to get out of the situation, would you take it?’ She said, ‘Yes.’” 

After the breakup, Figueroa and her four children by Ariel Castro – Anthony, Angie, Emily and Arlene  – went to live with Colon in 1995. According to Colon, Castro was furious, and after peppering the house with abusive phone calls, issued a threat to Colon. “He told me very clearly, ‘One day I’m going to get back at you and I’m going to ruin your life.’” Colon said that Castro waited for his moment “and then accused me of something that does the most damage to a person.” 

Castro made the molestation accusations in July 2004, two months after DeJesus vanished. “I think he did it to get police attention away from him,” said Colon. “By that point I think he already had all three (kidnapped) women under his roof.” 

NBCNews.com/Courtesy of Kayla Rogers

Arlene Castro poses for a picture in march of 2004.

Colon believes that his stepdaughters, Emily and Arlene, went along with their dad’s molestation charges because Castro had begun buying them things and doing them favors, even promising to get them a car, and because the girls resented Colon’s attempts to impose discipline. In court documents, he said that he had a “long history” with the two girls: “Defendant states that they are unruly and they don’t listen.” He also said that Emily was a drug user who at age 16 would stay away from the house for weeks at a time, according to court documents. 

Figueroa testified on Colon’s behalf at his 2005 bench trial. She said that Castro had started purchasing clothes for Arlene and had promised Emily an SUV. Figueroa also claimed that Castro, who had recently inherited some money, had promised her an expensive present as well. “Castro told me to go along with the complaints against Fernando Colon and he would buy me a new car,” said Figueroa in a pre-trial affidavit. “Castro was laughing and excited. … Castro believes that we will be together again.”

In the affidavit, she said that Arlene had “never discussed any inappropriate conduct between her and Fernando” and that as a stay-at-home mom, she had never witnessed any inappropriate sexual contact between Colon and his stepdaughters.

Arlene and Emily testified against Colon. But Anthony Castro, Ariel’s son, joined his mother in testifying on Colon’s behalf, saying he didn’t believe the charges of molestation.

Ex-wife sought restraining order
According to Chris Giannini, just before the trial began, Figueroa said that Ariel Castro had threatened to harm her if the girls did not testify at the trial. Arlene did not want to testify, said Giannini, and Emily was in Indiana with her adult boyfriend and didn’t want to return to Ohio. Figueroa sought a temporary restraining order, in which she inventoried years of alleged abuse at Castro’s hands: she alleged he had broken her nose twice, broken her ribs and caused a blood clot or tumor in her brain.

Giannini acted as an investigator for Colon in 2004 and 2005, helping his employee prepare his defense. At one point, he was able to arrange an interview with Castro to ask him about the allegations. Giannini said that Castro claimed that while he was driving Arlene and a friend around, the friend alleged that Fernando had stood over her while she was at a sleepover at Arlene’s house.

According to Giannini, Castro then claimed Arlene said that Colon had penetrated her digitally and demanded to know who she was having sex with.

“I had already heard somebody tell me the exact same story about Ariel,” said Giannini, who described the informant as “a family member.” “Right away I know what (Castro) is doing.  He’s projecting his own behavior on to Fernando.”

When the case against Colon went to trial at the end of August 2005, Ariel Castro took the stand to deny that he had ever abused Figueroa. Instead, he said, Figueroa had tried to get physical with him, once hitting her head on a door jamb in the process, which resulted in a trip to the hospital.

He also denied threatening Colon and Figueroa, and said he had gone to police immediately after hearing Arlene and her friend talking about Colon’s alleged inappropriate sexual behavior. When asked if anyone lived with him at his house on Seymour Avenue –  the address where police recovered Berry, DeJesus and Knight on Monday -- he said, “No.”

Kathleen DeMetz, Ariel Castro’s public defender in the kidnap and rape case, said she was unfamiliar with the Colon case and declined further comment.

The indictment of Colon originally contained 28 counts, including rape and kidnapping. On Sept. 6, 2005, the judge found Colon guilty on five counts of gross sexual imposition. He was sentenced to three years of probation, and is now a registered sex offender in Ohio.

“He hasn’t been able to get steady work in eight years,” said Giannini. “You can’t work in this field (security) with a felony on your record.” Colon also split up with Figueroa for good after the trial.

When news of Castro’s arrest broke, said Colon, his mother called him from Puerto Rico, sobbing. “She said, ‘I told you that all you had to do is have faith and something would come out,’” said Colon.

Now that Ariel Castro is in custody, said Colon, “I want my life back.” Colon and Giannini see an opportunity to challenge his conviction and repair his reputation. One of the first items on their agenda is speaking to Colon’s former stepdaughters to see if they will reconsider their testimony.

Talking to Emily Castro will require a trip to Indiana. Now 25, she’s currently serving a 25-year sentence in an Indiana state prison for the attempted murder of her daughter.

In April 2007, Emily slashed the then-11-month-old girl’s neck and then tried to slash her own wrists. At trial, defense attorneys argued that she was insane at the time of the attack. Nilda Figueroa appeared as a witness, testifying that Emily had struggled with depression for years and seemed paranoid since her daughter’s birth. She also said she had taken Emily to get mental help prior to the attempted murder.

Colon and Giannini also plan to contact Arlene, whose phone was not accepting calls on Wednesday.

Nilda Figueroa , however, can’t be enlisted in Colon’s bid for rehabilitation. She died in 2012 in Indiana at age 48.

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This story was originally published on Thu May 9, 2013 3:29 PM EDT

Win Mcnamee / Getty Images file

Director of National Intelligence James Clapper has ordered a broad review of how the U.S. handled information before the Boston Marathon bombing.

The nation's top intelligence official has ordered a review of the Boston Marathon bombing case amid questions about whether the U.S. should have known one of the suspects posed a threat.

Retired Gen. James Clapper, the director of national intelligence, has asked the inspector general who oversees the intelligence community to take a broad look at various agencies' handling of information they received long before the bombing.

“Based on what I've seen so far, the FBI performed its duties, Department of Homeland Security did what it was supposed to be doing, but this is hard stuff,'' President Obama said at a Tuesday news conference.

In 2011, Russia asked the U.S. to check into Tamerlan Tsarnaev because they suspected he was becoming radicalized. The FBI interviewed him but found no sign of terrorist activity.

His name and the name of his mother were put into intelligence databases that track possible terrorist ties, and U.S. agents were "pinged" when Tsarnaev flew last year to Russia, a trip that included time in the militant outpost of Dagestan.

Less than a year after he returned to the U.S., the 26-year-old ethnic Chechen and his younger brother, Dzhokhar Tsarneav, planted two bombs near the finish line of the April 15 marathon, killing three and wounding more than 200 more people, authorities said.

Since then, there's been debate about whether Russia gave the U.S. enough information about Tsarnaev and whether the FBI and CIA should have been more thorough in vetting Tsarnaev.

“It’s not as if the FBI did nothing,” Obama said. “They not only investigated the older brother, they interviewed him.”Obama said that while there were “no signs” of terrorist tendencies then, investigators want to know if something happened later to trigger Tsarnaev’s radicalization and what the U.S. can do to detect such shifts in the future.

He said Russia has been “very cooperative” since the attack, but also noted that “old habits die hard” and that some suspicion between between the two countries’ intelligence agencies, dating back decades, has survived.

He portrayed the review as an effort to improve intelligence, not find fault with anyone.

“What Director Clapper is doing is standard procedure around here,” Obama said.

Still, one U.S. counter-terrorism official said some in the intelligence community are "furious" about Clapper's probe, because it suggests that mistakes were made.

Tamerlan Tsarnaev was killed during a shootout with police. His brother was arrested after a manhunt that shut down Boston for a day and has been charged with using a weapon of mass destruction.

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Cambridge Police Dept.

Tamerlan Tsarnaev is seen in a booking photo from a 2009 arrest in Cambridge, Mass.

This story was originally published on Tue Apr 30, 2013 10:54 AM EDT

The White House said Thursday that the U.S. believes "with some degree of varying confidence" the Syrian government has used chemical weapons — specifically the nerve agent sarin — against its own people.

A letter from the White House to members of Congress said the assessment was based on "physiological samples" but called for a United Nations probe to corroborate it and nail down when and how they were used.

"We are continuing to do further work to establish a definitive judgement as to whether or not the red line has been crossed and to inform our decision-making about what we'll do next," a White House official said. 

"All options are on the table in terms of our response," the official added.

Secretary of State John Kerry told reporters at the Capitol that the U.S. believes chemical weapons were used twice, but the letter doesn't specify that.

"Our intelligence community does assess with varying degrees of confidence that the Syrian regime has used chemical weapons on a small scale in Syria, specifically the chemical agent sarin," the letter said.

"We do believe that any use of chemical weapons in Syria would very likely have originated with the Assad regime," it added.

"Thus far, we believe that the Assad regime maintains custody of these weapons, and has demonstrated a willingness to escalate its horrific use of violence against the Syrian people."

Defense Secretary Chuck Hagel said he had not seen the evidence supporting the assessment, but added that use of chemical agents "violates every convention of war."

Sarin is a man-made nerve agent that has been used in terrorist attacks in Japan and possibly during the Iran-Iraq War in the 1980s, according to the U.S. Centers for Disease Control. In large doses, it can cause convulsions, paralysis and death.

The U.S. has long believed that Syria was stockpiling chemical weapons. Intelligence reports indicate that it has sarin and the nerve agent tabun along with traditional chemicals like mustard gas and hydrogen cyanide. A 2011 CIA report said Syria was also developing the potent nerve agent VX, which could render a city uninhabitable for days.

Syria's information minister, Omran al-Zoubi, said in an interview with Russian TV that the government has not and will not use chemical weapons and blamed potential evidence of their existence on "armed terrorist groups," the state news agency reported.

A spokesman for the rebel Free Syrian Army, Fahd Almasri, claimed Syria has launched chemical attacks in nine places and was poised to do so again at the Lebanon border and in Damascus "when Assad knows he is finished."

"Now is the moment to find a solution very quickly," Almasri told NBC News in a phone interview.

President Obama has said the verified use of chemical weapons by the regime would be a "red line" and a "game-changer" for U.S. and international military intervention in the Syrian civil war.

"Precisely because the President takes this issue so seriously, we have an obligation to fully investigate any and all evidence of chemical weapons use within Syria," said the letter, which was signed by Obama's legislative director, Miguel Rodriguez.

The letter was a response to a request from a bipartisan group of senators who asked the White House for answers after the Israeli military’s top intelligence analyst cited photographs of people "foaming from the mouth” as evidence of chemical weapons use.

Sen. Bob Corker, R-Tenn., ranking member of the Senate Foreign Relations Committee, called the development “deeply troubling.”

“While more work needs to be done to fully verify this assessment…it is becoming increasingly clear that we must step up our efforts,” Corker said.

“I should make clear, however, that it if it comes to the use of military force, before the president takes any action to commit U.S. forces to any effort in Syria or elsewhere, I expect him to fully consult with the Senate and seek an authorization for the use of military force."

Sen. Dianne Feinstein, chair of the Senate Intelligence Committee, said the assessment could spark a dangerous reaction from Damascus.

"I am very concerned that with this public acknowledgement, President Assad may calculate he has nothing more to lose and the likelihood he will further escalate this conflict therefore increases," Feinstein said.

The White House official called for a high level of scrutiny — but also caution.

"Given our own history with intelligence assessments, including intelligence assessments related to weapons of mass destruction, it's very important that we are able to establish this with certainty and that we are able to present information in a way that is airtight," the official said.

NBC News' Kasie Hunt, Kelly O'Donnell, Robert Windrem and Charlene Gubash contributed to this story

Slideshow: Syria uprising

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This story was originally published on Thu Apr 25, 2013 11:56 AM EDT

One of the Boston Marathon bombing suspects landed in at least one low-level intelligence database two years ago, and the system alerted U.S. agents when he flew to Russia last year, federal officials told NBC News on Wednesday.

But federal authorities took no action against Tamerlan Tsarnaev because the FBI had already interviewed him at the request of the Russian government and found no sign of terrorist activity, the officials said.

The officials said Russia asked for information about Tsarnaev twice in 2011, once early in the year from the FBI and once in September from the CIA, because the Russians said they had reason to believe he was becoming a radical.

When the FBI turned up nothing after the first request, it asked Russia for further information, but Russia never supplied it, the officials said. The FBI asked again after the September request to the CIA, and Russia again failed to respond, they said.

The FBI in early 2011 opened a threat assessment, its lowest-level investigative step, which automatically put an entry in a low-level intelligence database, the Treasury Enforcement Communications System, the officials told NBC News.

In addition, Rep. Michael McCaul, R-Texas and the head of the House Homeland Security Committee, said Wednesday that Tsarnaev turned up in a database maintained by the National Counterterrorism Center.

That database, the Terrorist Identities Datamart Environment, is almost a half-million names long. It is used to craft smaller terror watch lists, including the no-fly list, but does not by itself stop anyone from traveling.

Some Republicans have questioned whether intelligence agencies adequately shared information about Tsarnaev, who with his brother is accused of killing three people and injuring more than 200 with bombs at the marathon last week.

Slideshow: Aftermath and reaction following Boston bombings

Heightened security, empty streets and memorials mark the the days after the Boston Marathon bombings.

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“We talked a lot about connecting the dots and stovepipes after 9/11,” McCaul said on MSNBC's “The Daily Rundown.” “Here we are 12 years later and it’s still not working.”

When Tsarnaev flew to Moscow last January, the system “pinged,” in the language of intelligence officials. Those “pings” are common, one official said, and a federal agent might get 30 or 40 per day.

Because the FBI had checked out Tsarnaev, including interviewing him and members of his family, the “ping” led to no further action, the federal officials said.

“Without a tool to cut down on the number of false positives, the FBI would be chasing its tail if it tried to deeply investigate anyone who even remotely ‘pings’ the system,” said Evan Kohlmann, an NBC News terrorism analyst and former consultant to the FBI and Defense Department. “There just aren’t enough FBI agents and analysts to accomplish that task.”

In addition, he said, FBI agents are short on resources, particularly after mandatory federal budget cuts, and Congress has failed in its oversight responsibility to make sure the bureau is advancing its computer tracking capabilities.

“So, in short, the system probably didn’t work here — but there is plenty of blame to go around,” Kohlmann said.

Investigators want to know what Tsarnaev, who is of Chechen origin with a U.S. green card, was doing in Russia for the first half of last year.

The trip coincided with what appears to be increasing agitation in recent years, including posting radical Islamic videos on a YouTube page and disrupting services at a Cambridge, Mass., mosque.

Dzhokhar Tsarnaev, the surviving suspect, has told investigators that he and his brother carried out the attack, that they acted alone and that they did it to defend Islam after the U.S. wars in Iraq and Afghanistan.

Senators should have a chance Thursday to hear more about the Boston investigation at a regularly scheduled administration briefing. Senators indicated Wednesday that the officials from the FBI and the Department of Homeland Security will be there.

Rep. William Keating, a Democrat who represents Boston, said on MSNBC’s “Hardball” that Congress should examine how the United States and Russia shared, or failed to share, information. But he appeared satisfied with how the FBI has handled the case.

“They played it by the book,” he said.

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This story was originally published on Wed Apr 24, 2013 6:06 PM EDT

Any major bomb investigation is an elaborate, high-tech piece of choreography by city, state and federal agencies with two goals: helping investigators figure out who built and planted the explosive device or devices and preserving evidence so that they can be brought to justice.

And the forensic investigation established soon after the twin blasts at Monday’s Boston Marathon has already begun yielding results. On Tuesday afternoon, law enforcement officials had indications that the bombs were made from pressure cookers filled with explosives, nails and BBs, and that they were placed in black nylon bags.

The work is far from over. Fragments, blood smears and explosive residue from the Boylston Street crime scene -- all of it will be carefully cataloged and examined. Every frame of video and every photo will be scrutinized, a mammoth undertaking in light of authorities’ pleas for spectators to turn over their images.

There’s other evidence to consider, too. A smell of sulfur in the air could indicate smokeless black powder was used. The size and color of a fireball could point to certain additives. Certain bomb mechanisms -- a type of fuse, a type of timer -- could be signatures of a particular group.

Alex Trautwig/Getty Images

A member of the bomb squad investigates a suspicious item on the road near Kenmore Square after two bombs exploded during Boston Marathon on April 15.

"In an investigation of this nature, no detail is too small," Attorney General Eric Holder said Tuesday.

As the data piles up, investigators will begin to get some idea of who was behind the horrific act: an amateur or a professional bomb-maker, a home-grown lone wolf or a foreign-sponsored terrorist gang.

Early indications were pointing toward a sophisticated creator, as the bombs were designed and placed to act like a "homemade claymore," a powerful, directional anti-personnel device, sources involved in the investigation said.

These and other sources say that the triggering mechanism appears to have included a battery pack and a circuit board, the elements they said of a sophisticated triggering mechanism. Both of those elements were recovered at the scene.

"It appeared to be built from scratch but with a sophisticated triggering mechanism. And frankly, at the end of the day, all bombs are crude devices, and it is the way they are triggered that can be sophisticated," said one official with strong knowledge of explosives. "They functioned as designed."

In these kinds of investigations, the forensic process begins as soon as police have done what they can to preserve human life and clear the area, with bomb technicians and emergency service cops canvassing for devices that may not have exploded yet.

Protection from contamination
In Boston, officials confirmed they used controlled explosions -- usually done with water cannons -- on five suspicious packages that turned out not to be bombs.

Afterward, uniformed officers -- in Boston's case, the National Guard -- secure the perimeter of the blast site to protect the evidence from contamination until the specialists can bag, tag and transport it to a central location, where a prosecutor would ideally be supervising the chain of custody, local and federal officials say.

Boston's FBI Special Agent in Charge Richard DesLauriers said that recovery effort officially began Tuesday morning.

In these investigations, the entire area is photographed and investigators begin a grid search, working outward from the seat of the blast, swiping fragments for explosive residue and gathering anything that could be a clue. In Boston, debris has been found on roofs and embedded in buildings. What’s recovered will be sent to the FBI lab in Quantico, where it will eventually be logged on a grid, according to law-enforcement officials.

The painstaking work can have big payoffs.

If authorities can identify a type of explosive, they can try to trace where it might have been purchased. 

As House Homeland Security Chairman Michael McCaul, R-Texas, noted, if the probe reveals the bomb was set off by a cellphone call, investigators can track all the calls made at exactly that moment.

Private and city surveillance cameras can show the color and density of the smoke plume -- details that can point to bomb size and ingredients.

Damage can tell a tale
To the trained eye, damage to the area and to the victims also yield important information. In Boston, pockmarks on the buildings pointed to a bomb packed with BBs. The gruesome injuries -- legs torn from bodies -- would indicate the bomb was close to the ground, experts say. The absence of widespread ear and lung injuries is associated with a low-explosive device.

Blood from the scene is also collected. The lab can later compare the samples to the victims' types to determine if there's a swab that has no match and could belong to a suspect.

If investigators are lucky, within 12 hours they will have enough fragments to pinpoint certain aspects of the bomb -- as has happened in the Boston case. The FBI then begins building a facsimile of the device.

Boston bombing investigators were working to identify the type of timer -- whether it was a cellphone alarm, for instance -- and verify other components and substances used.

The manpower required for such tasks is massive. A probe like the one in Boston could easily involve more than 100 people in forensic collection and analysis.

In Boston, the FBI has taken the lead. The Bureau of Alcohol, Tobacco and Firearms announced it was sending 30 specialists to the city. There will be experts in dental work, DNA, blood-pattern analysis and digital video analysis working the case. Local and out-of-town agencies devoted bomb squad and forensic personnel to the investigation.

Typically, 36 hours after a bombing the forensic teams will have collected and mapped what they can and will consider releasing the scene. The hope is that by then they will also have someone in custody or some idea of who it is they're hunting.

Richard Esposito is the author of “Bomb Squad: A Year Inside the Nation’s Most Exclusive Police Unit”.

Slideshow: Boston Marathon explosions

Charles Krupa / AP

See images from the scene of the explosions.

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This story was originally published on Wed Apr 17, 2013 3:39 AM EDT

A New York City cardiologist with offices on Fifth Avenue and in New Jersey admits he intentionally misdiagnosed up to 80 percent of his patients with heart problems so he could collect millions in extra Medicare money. 

 Dr. Jose Katz, 68, pleaded guilty to falsifying charts diagnosing patients with angina and other heart ailments so he could prescribe extra tests and treatments when hundreds of patients did not need them.

See original story at NBCNewYork.com

Prosecutors said it was the largest fraud ever executed by a single doctor in New York or New Jersey. 

"After years of prominence in his field, Jose Katz will now be remembered for his record-setting fraud," said U.S. Attorney Paul Fishman.

In court Wednesday he agreed his actions could have caused "serious bodily harm" to his patients. He and his lawyer disagreed when prosecutors said some patients were at risk of death due to his actions.

In all, Katz admitted his scheme took in over $19 million. 

Katz's crimes went on from at least 2004 through 2012. His resume said he is affiliated with NewYork-Presbyterian Hospital, but a spokeswoman said he has not been linked there since 2003.

Fishman said many patients who were exploited went to Katz's clinics, called Cardio-Med Services in Union City, Paterson and West New York.  He also ran clinics called Comprehensive Healthcare in Manhattan and Queens. 

Katz said he performed many so-called EECP procedures based on false diagnoses to overbill Medicare and private insurers like Blue Cross and Aetna.   

In court, Katz told the judge as a doctor he had "done everything he could to help patients."  The judge told him he would have time to speak at sentencing set for July 23. After the court hearing, Katz and his attorney, Blair Zwillman, left the courthouse admitting mistakes were made but insisting Katz always cared for his patients.    

See court document on the case in PDF

Katz faces up to 10 years in prison on the conspiracy to commit health care fraud charges. He also admitted creating a no-show job in his office in order to rip off more than $250,000 in Social Security benefits. 

Katz was born in Cuba but is a U.S. citizen. Prosecutors said he spent $6 million advertising on Spanish-language television and radio to try to lure in patients. 

Fishman said investigators are attempting to contact all the patients affected by the fraud, who can also reach out to the New Jersey FBI or U.S. attorney's offices for additional information. 

Related story at NBCNewYork.com: 4 charged in alleged medical billing scam

This story was originally published on Wed Apr 10, 2013 3:47 PM EDT

Search warrants released Thursday laid bare the extent of Newtown school massacre suspect Adam Lanza's arsenal. Here is a catalog of the weaponry found at the school where 20 children and six staffers were killed and at the home he shared with his mother, who was also murdered:

At the school:

1 Bushmaster .223 caliber model XM15 rifle with a 30-round magazine

1 Glock 10mm handgun

1 9mm Sig Sauer P226 handgun

1 Saiga 12 shotgun with two magazines containing 70 rounds

6 30-round magazines, three of them emptied

At the home:

Guns:

1 Enfield bolt-action .323 rifle

1 Savage Mark II .22 caliber rifle with magazine, 3 live rounds, 1 spent cartridge

1 black marksman BB gun

Ammunition:

5 Winchester 12-gauge shotgun shells cut open, with buckshot

1 white plastic bag with 30 Winchester 12-gauge shotgun shells

1 can with .22 caliber and .45 caliber bullets

8 boxes of Winchester Windcat .22 caliber bullets, 50 rounds per box

20 "Estate" 12-gauge shotgun shells

4 boxes of SB buckshot 12-gauge, 10 round per box

1 box of Lightfield 12-gauge slugs

1 box of 20 Prvi Partizan 303 British rifle cartridges

1 box of 20 Federal 303 British rifle cartridges

2 boxes of .22 long rifle Blazer rounds, 50 each box

1 box with numerous rounds of Winchester .45 caliber bullets

2 boxes of 50 rounds of PPU .45 caliber automatic

1 box of 20 rounds for Remington .223 caliber

3 boxes of Blazer 40 S&W, 50 rounds each

2 boxes of Winchester 5.56 mm, 20 rounds each

1 box of Magtech 45ACP with 30 rounds

1 empty Box of SSA 5.56 mm

1 box of Fiocchi .45 auto with 48 rounds

80 rounds of CCI .22 long rifle

6 boxes of PMC .223 rem, 20 rounds each

6 Winchester 9 pellet buckshot shells, 12-gauge

2 Remington 12-gauge slugs

3 Winchester .223 rifle rounds

31 .22 caliber rounds

2 boxes of Underwood 10 mm auto, each with 50 rounds

130 rounds of Lawman 9mm Luger

2 spent shell casings for Glock 10mm

1 empty box of Gold Dot 9mm Luger

2 empty boxes of Winchester 9mm Luger

1 box of Underwood 10mm auto with 34 rounds

1 box of 29 miscellaneous 9mm rounds

1 spent .22 shell casing

1 small plastic bag containing numerous .22 caliber bullets

1 tan bag with numerous Blazer .45 caliber bullets

1 box of Blazer .22 long rifle with 50 rounds

1 box PPU 303 British cartridges with 9 rounds

2 Winchester 9mm rounds

2 brass-colored shell casings

1 small caliber bullet (live round) labeled C

Magazines:

1 Promag 20-round 12-gauge drum magazine

1 MD Arms 20-round 12 gauge drum magazine

3 AGP Arms 12-gauge shotgun magazines

1 Surefire GunMag magazine with 8 rounds of Winchester 12-gauge, 9-pellet buckshot

2 AGP Arms 12-gauge shotgun magazines, taped together, each with 10 rounds of Winchester 9-pellet buckshot

2 empty Ram Line magazines for Ruger 10-22

1 AGP Arms Gen 2 12-gauge shotgun magazine with 10 rounds of Winchester 12-gauge, 9-pellet buckshot

1 clear plastic Ramline magazine for an AR 15

1 magazine with 10 rounds of .223 bullets

Knives:

Metal bayonet

1 6-foot-10-inch wood-handled two-sided pole with a blade on one side and a spear on the other

1 Samurai sword with a 28-inch blade and sheath

1 Samurai sword with a 21-inch blade and a sheath

1 Samurai sword with a 13-inch blade and sheath

1 knife with a 12-inch blade and sheath

1 wooden-handle knife with a 7.5-inch blade and sheath

1 wooden-handle knife with a 10-inch blade

1 knife with a 5.5-inch blade and sheath

1 black-handled knife with a 7-inch blade and sheath

1 black rubber-handled knife with 9.5-inch blade and sheath

1 white and brown-handled knife with 5-inch blade and sheath

1 brown wood-handled knife with a 10.25-inch blade

1 Panther brown-handled folding knife with a 3.75 inch blade

1 small blue folding knife

Gear:

1 Volcanic .22 starter pistol wth 5 live rounds and 1 expended round

Leightning L3 ear protection

Peltor ear plugs

Simmons binoculars

Uncle Mike's Sidekick nylon holster

Box for vest accessories

Leather dual magazine holder

Black leather handgun holster

High Sierra fanny pack

Numerous paper targets

1 cardboard targets

1 Bushnell sport view rifle scope

Plastic bag of miscellaneous parts

Safariland holster paperwork

Glock handgun manual

MD-20 20-round shotgun magazine manual

MD Arms V-Plug guide

Bushmaster XM15 and C15 instruction manual

Savage Arms bolt-action rifle manual

Glock paperwork

Miscellaneous:

Adam Lanza's National Rifle Association certificate

Nancy Lanza's NRA certificate

Three photographs with images of what appears to be a deceased human covered with plastic and what appears to be blood

Holiday card with a check from Nancy Lanza to Adam Lanza for purchase of C183 firearm

1 digital print of a child and various firearms

1 military-style uniform

Handwritten notes with addresses of local gun shops

Receipts and emails documenting firearm and ammunition supplies

Blue folder labeled “guns” with receipts and paperwork

Paperwork titled "Connecticut Gun Exchange Glock 20SF 10mm" dated 12-21-11

Sandy Hook report card for Adam Lanza

New York Times article on a 2008 shooting at Northern Illinois Unversity

Books: “Look me in the Eye: My Life with Asperger’s;” “Born on a Blue Day: Inside the Mind of an Autistic Savant;” “NRA Guide to Basics of Pistol Shooting;” “Train Your Brain to Get Happy”

1 Seagate Barracuda 500gb hard drive, damaged

1 custom-built desktop computer, no hard drive

1 Microsoft Xbox with partially obliterated serial number

One cotton swab of blood-like substance

1 tan sheet with blood-like substance

1 tan fitted sheet with blood-like substance

1 striped towel with blood-like substance

Related: 

Lanza fired 155 bullets in less than five minutes, prosecutor says

Search warrants: Read them, search them

This story was originally published on Thu Mar 28, 2013 11:19 AM EDT