Brothers Tamerlan and Dzhokhar Tsarnaev planted two homemade pressure cooker bombs that detonated near the finish line of the race 14 seconds and 210 yards (190 m) apart.

[27] Immediately after the bombing occurred and medically injured people were transported, the police closed a 15-block area around the blast site; this was reduced to a 12-block crime scene the next day.

[29] The Massachusetts Emergency Management Agency suggested that people trying to contact those in the vicinity use text messaging instead of voice calls because of the crowded cell phone lines.

[44] Google Person Finder activated their disaster service under Boston Marathon Explosions to log known information about missing people as a publicly viewable file.

Representative Peter King, a member of the House Intelligence Committee, said: "I received two top secret briefings last week on the current threat levels in the United States, and there was no evidence of this at all.

"[50] Evidence found near the blast sites included bits of metal, nails, ball bearings,[51] black nylon pieces from a backpack,[52] remains of an electronic circuit board and wiring.

[85] A later report by Harvard Kennedy School's Program on Crisis Leadership concluded that lack of coordination among police agencies had put the public at excessive risk during the shootout.

[120] On the evening of April 19, after the shelter-in-place order had been lifted, David Henneberry, a Watertown resident outside the search area, noticed that the tarpaulin was loose on his parked boat.

[126] Dzhokhar Tsarnaev was arrested at 8:42 p.m.[127][128] and taken to Beth Israel Deaconess Medical Center, where he was listed in critical condition[129] with gunshot wounds to the head, neck, legs, and hand.

[132] The confusion was caused in part by a lack of clearly identified and coordinated law enforcement command of the thousands of officers from surrounding communities who self-deployed into the Watertown area during the events.

[137] United States Senators Kelly Ayotte, Saxby Chambliss, Lindsey Graham, and John McCain, and Representative Peter T. King suggested that Dzhokhar Tsarnaev, a U.S. citizen, should be tried as an unlawful enemy combatant rather than as a criminal, potentially preventing him from obtaining legal counsel.

[157] The trial began on March 4 with Assistant U.S. Attorney William Weinreb describing the bombing and painting Dzhokhar as "a soldier in a holy war against Americans" whose motive was "reaching paradise".

[158] Defense attorney Judy Clarke admitted that Dzhokhar Tsarnaev had placed the second bomb and was present at the murder of Sean Collier, the carjacking of Dun Meng, and the Watertown shootout, but she emphasized the influence that his older brother had on him, portraying him as a follower.

The First Circuit vacated the death sentence and three of the other thirty convictions against Tsarnaev, and ordered a new penalty phase jury trial with fresh jurors, leaving the decision of a new change of venue to the District Court.

[167][35] According to FBI interrogators, Dzhokhar and his brother were motivated by extremist beliefs but "were not connected to any known terrorist groups", instead learning to build explosive weapons from an online magazine published by al-Qaeda affiliates in Yemen.

[16] They further alleged that "Dzhokhar and his brother considered suicide attacks and striking the Boston Pops Fireworks Spectacular on the Fourth of July";[168] but ultimately decided to use remotely-activated pressure cooker bombs and other IEDs.

[221] On April 15, several people who were near the scene of the blast were taken into custody and questioned about the bombing, including a Saudi man whom police stopped as he was walking away from the explosion; they detained him when some of his responses made them uncomfortable.

[241][242]Kadyrbayev and Tazhayakov were indicted by a federal grand jury on August 8, 2013, on charges of conspiracy to obstruct justice for helping Dzhokhar Tsarnaev dispose of a laptop computer, fireworks, and a backpack after the bombing.

[286] Law enforcement, local and national politicians, and various heads of state reacted quickly to the bombing, generally condemning the act and expressing sympathies for the victims.

[305] Five years after the bombing, The Boston Globe reported all of the items from the memorials were being housed in a climate controlled environment, free of charge, by the storage company, Iron Mountain in Northborough, Massachusetts.

[309][310] One study conducted by the Institute for Public Service at Suffolk University in Boston, Massachusetts, recorded the mental health and emotional response of various survivors, for three years following the bombing.

Jamie Pitblado, vice-president of promotions for The Vancouver Sun and The Province, said the money would go to One Fund Boston, an official charity that collected donations for the victims and their families.

Senators Saxby Chambliss and Richard Burr reported that Russian authorities had separately asked both the FBI (at least twice: during March and November 2011) and the CIA (September 2011) to look carefully into Tamerlan Tsarnaev and provide more information about him back to Russia.

[345] FSB secretly recorded phone conversations between Tamerlan Tsarnaev and his mother (they vaguely and indirectly discussed jihad) and sent these to the FBI as evidence of possible extremist links within the family.

[citation needed] However, while Russia offered US intelligence services warnings that Tsarnaev planned to link up with extremist groups abroad, an FBI investigation yielded no evidence to support those claims at the time.

[346][failed verification] On April 19, 2013, the press secretary of the head of the Chechen Republic, Ramzan Kadyrov, issued a statement that, inter alia, read: "The Boston bombing suspects have nothing to do with Chechnya".

[354] The National Lawyers Guild and some news outlets questioned the constitutionality of the door-to-door searches conducted by law enforcement officers looking for Dzhokhar Tsarnaev.

Theorists also cite the fact that the FBI has been criticized for an alleged practice under former director James Comey of encouraging confidential informants to attempt terrorist attacks.

Since these stories often have unintended consequences, we ask the media, particularly at this early stage of the investigation, to exercise caution and attempt to verify information through appropriate official channels before reporting.

[388][389]The decision to release the photos of the Tsarnaev brothers was made in part to limit damage done to those misidentified on the Internet and by the media, and to address concerns over maintaining control of the manhunt.