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.
Cambridge Police Dept.
Tamerlan Tsarnaev is seen in a booking photo from a 2009 arrest in Cambridge, Mass.
REUTERS
Boston Marathon bomb scene pictures taken by investigators show the remains of an explosive device. The photos were produced by the Joint Terrorism Task Force of Boston.
Symantec Corp.
This pop-up screen appears to come from the FBI.
Symantec Corp
In this version of the scam, the virus activates the victim's webcam and displays an image from it on the screen, making the warning even more unnerving
NBC's Michael Isikoff reports on what a source, inside the hospital room with Dzhokhar Tsarnaev, is telling him about Tsarnaev's interaction with investigators. NBC analyst Roger Cressey also joins to discuss what authorities are now saying about the Tsarnaev brothers' possible plans for an attack on New York City.
Handout / FBI via Reuters
Dzhokhar Tsarnaev, 19, has been charged in the Boston Marathon bombing.
In a press conference regarding the news that the Boston Marathon bombers were intending on striking New York's Times Square, Mayor Michael Bloomberg touts camera technology and vows to continue to keep people safe.
Police are beginning to make use of cutting-edge technology that could help officers spot a bomb before it goes off. NBC's Jeff Rossen reports.
Cambridge Police Department
Tamerlan Tsarnaev is seen in a booking photo from a 2009 arrest in Cambridge, Mass.
Sen. Lindsey Graham gives his viewpoint on whether the U.S. Dept. of Homeland Security did enough to follow up on leads relating to Boston bombing suspect Tamerlan Tsarnaev.
A look back at the conflict that has overtaken the country.
Defense Secretary Chuck Hagel told reporters in Abu Dhabi that the United States has "a reasonable amount of confidence that some amount of chemical weapons was used" by the Syrian government.
AP
These undated file photos provided by the City County Bureau of Identification in Wake County, N.C., show from left: Daniel Patrick Boyd, Hysen Sherifi, Mohammad Omar Aly Hassan and Ziyad Yaghi. Authorities claim the group and others, including Boyd's sons, were gearing up for a "violent jihad" overseas.
Rich Pedroncelli / ASSOCIATED PRESS
Umer Hayat, left and his son, Hamid, of Lodi, Calif., were convicted in a 2005 terrorism case.
Hannah Rappleye / NBC News
A bullet pierced a tree alongside Laurel Avenue in Watertown, Mass., the result of gunfire aimed east toward the Tsarnaev brothers.
Hannah Rappleye / NBC News
Stains on the pavement where Tamerlan Tsarnaev, 26, fell on Laurel Street early last Friday. During a dramatic gunfight with police, Tsarnaev was mortally wounded and dragged by a vehicle driven by his brother, Dzhokhar, 19.
Hannah Rappleye / NBC News
Laurel Street in residential Watertown, Mass., was the scene of a dramatic gunfight early last Friday between law enforcement and two men that authorities say were Tamerlan Tsarnaev, 26, and his brother, Dzhokhar Tsarnaev, 19.
Hannah Rappleye / NBC News
Damage to a fence alongside Laurel Avenue in Watertown sustained during a dramatic gunfight early Friday morning. The bullets were aimed east toward the Tsarnaev brothers.
The bombing suspects engage police in Watertown in a fierce firefight, captured on camera.
NBC's Pete Williams joins Andrea Mitchell Reports to share the latest in the investigation.
There are growing questions as to whether or not U.S. intelligence officials have done more when investigating Tamerlan Tsarnaev prior to the Boston bombing. NBC's Pete Williams reports.
Heightened security, empty streets and memorials mark the the days after the Boston Marathon bombings.
Trains originating in the U.S. were among the possible targets, NBC News has learned. Authorities say there was never any imminent danger to the public. NBC's Stephanie Gosk reports.
Stephane Jourdain / AFP - Getty Images file
An Amtrak police officer and a sniffer dog patrol at Union Station in Washington on May 6, 2011, five days after Osama bin Laden was killed in Pakistan. Intelligence seized from his compound showed al Qaeda pondered strikes on U.S. trains on the 10th anniversary of the Sept. 11 attacks, U.S. officials said.
Brendan Mcdermid / Reuters file
An Amtrak police officer watches as passengers prepare to board a train at New York's Penn Station on April 19.
The siblings of MIT Police Officer Sean A. Collier, 27, who was killed April 18, describe their brother on the TODAY Show.
Vice President Biden spoke at the memorial for slain MIT police officer Sean Collier and condemned terrorism, saying, "Boston, you sent a powerful message to the world."
Thousands of mourners attended a memorial service for Sean Collier, the MIT police officer who authorities say was gunned down by the Boston marathon bombing suspects. His stepbrother Rob Rogers told the crowd, "People have asked me, if Sean were here, what would he think? Are you kidding me? He would love this. You've got sirens. Flashing lights. Formations. People saluting. Bagpipes. Taps. The American flag. He would have loved it. He was born to be a police officer, and he lived out his dreams."
TODAY
Officer Sean A. Collier, 27, of the MIT Police was killed April 18 in Cambridge.
Dominick Reuter / Reuters
Heightened security, empty streets, and memorials mark the the day after the Boston Marathon bombings.
Alan Spearman / The Commercial Appeal file
Driver Jimmy Vinson waits for the scene of a motorcycle accident to be cleared on March 26, 2012, in Memphis, Tenn. No one died in this crash, but more than 5,000 riders were killed nationwide last year, according to preliminary accident data.
Brendan Smialowski / AFP - Getty Images file
Wayne LaPierre, chief executive officer of the National Rifle Association, speaks during a hearing of the Senate Judiciary Committee on Capitol Hill on Jan. 30 in Washington, D.C. The NRA spent more on lobbying in the first quarter than it had on any quarter ever.
Gazeta / AP file
A special forces officer takes a hostage out of the theater where hundreds were held by Chechen gunmen, in Moscow, Saturday, Oct. 26, 2002.
Oleg Nikishin / AFP - Getty Images file
Chechen volunteer checks a piano 27 December in one of the main streets of Grozny, where Russian jets have conducted bomb attacks over the past several days.
Richard Engel, NBC News chief foreign correspondent, talks with Rachel Maddow about the likely interrogation of Marathon bombing suspects Dzhokhar Tsarnaev, and how the public celebration of the law enforcement victory in this case undermines what would have been a bragging point for recruiters of terrorists worldwide.
The FBI invokes the "public safety exception" with Boston bombings suspect Dzhokhar Tsarnaev. Chris Hayes breaks down what this means.
While the crisis is over, the investigation of what motivated the suspects is just beginning. NBC's Michael Isikoff reports.
AP
Tamerlan Tsarnaev, left, was killed by police. Dzhokhar Tsarnaev was captured and will be interrogated by a special team of investigators.
Among the music videos that Tamerlan Tsarnaev posted on his YouTube account was this one featuring Italian-American rapper Vinnie Paz.
Several videos by radical Australian preacher Feiz Mohammed were posted on Tamerlan Tsarnaev's YouTube page.
Stephen Morton / AP file
The Imperial Sugar Co. plant on the Savannah River in Port Wentworth, Ga., is seen Feb. 8, 2008, a day after an explosion and fire there killed 14 people.
Ted S. Warren / AP file
Security guards staff a gate at a Tesoro Corp. refinery in Anacortes, Wash., on April 2, 2010, after a fatal explosion and fire.
U.S. Coast Guard / Reuters file
Fire crews battle the blaze aboard the oil rig Deepwater Horizon off Louisiana on April 21, 2010. Three years later, there is still no report by the Chemical Safety Board on the disaster.
Eric Risberg / AP file
Smoke pours from a fire at the Chevron Richmond Refinery, seen behind Alcatraz Island in San Francisco, on Aug. 6. Chemical Safety Board officials say their response to that incident delayed work on reports about other accidents.
Reuters
Boston Marathon bomb scene photos taken by investigators show the remains of an explosive device. The photos were provided by the Joint Terrorism Task Force of Boston on Tuesday.
Shannon Stapleton / Reuters
Heightened security, empty streets, and memorials mark the the day after the Boston Marathon bombings.
FBI via AP
This image from the FBI shows the remains of a pressure cooker that the FBI says was part of one of the bombs that exploded during the Boston Marathon.
In the wake of the Boston bombings, law enforcement officials are keeping a close eye on websites that provide instructions on how to make destructive devices. Authorities are now using these sites to track down potential terrorists. NBC's Lisa Myers reports.
Charles Krupa / AP
See images from the scene of the explosions.
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.
NBC News Terrorism Expert Michael Leiter explains investigators search through photographs and video as looking for "a needle in a haystack" in piecing together who's responsible in the bombing at the Boston Marathon.
Investigators have begun the process of recovering tiny pieces of bombs to learn how they were made. So far, they know the bombs were made from pressure cookers filled with ball bearings and nails -- a method used for decades in terror bombings. But no suspects are in custody and investigators are asking the public for help. NBC's Pete Williams reports.
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