Lowell Sun and FBI, File, AP Photos
BOSTON — A surveillance video shows a man prosecutors say is Dzhokhar Tsarnaev placing a bomb near the finish line of the Boston Marathon, just yards from where an 8-year-old boy was killed when it exploded.
A hand-scrawled confession condemning U.S. actions in Muslim countries was found on the inside wall of the boat where Tsarnaev was captured four frantic days later.
A year after twin pressure cooker bombs shattered the marathon and paralyzed the area for days, federal prosecutors say they have a trove of evidence ready to use against the surviving suspect, but many questions remain.
What roles did Dzhokhar Tsarnaev and his older brother, Tamerlan, play in planning and orchestrating the attack? Would they really have launched a second attack in New York? Did federal authorities underreact to a warning from Russia that Tamerlan Tsarnaev was becoming radicalized?
With Tamerlan Tsarnaev killed in a police shootout days after the attack, some of those questions may never be fully answered.
"The obvious one is the motivation and how could two young men who were in a country that, from all appearances, was very good to them end up this radical," said former Boston Police Commissioner Ed Davis, who helped lead the investigation.
The bombings last April 15 killed three people and injured more than 260 near the finish line of one of the world's most famous marathons. At least 16 people lost limbs.
Dzhokhar has pleaded not guilty to a 30-count federal indictment that carries the possibility of the death penalty.
The brothers, ethnic Chechens who lived in the former Soviet republic of Kyrgyzstan and the Dagestan region of Russia, settled in Cambridge, outside Boston, after moving to the U.S. as children with their family more than a decade ago.
Dzhokhar's defense team, which includes two of the nation's top anti-death penalty lawyers, appear to be building a case that Tamerlan, 26, was the driving force behind the bombings. In court documents, they've focused on Dzhokhar's young age — 19 at the time of the bombings — and the influence his older brother had on him.
A congressional report released last month said U.S. intelligence agencies missed a chance to detain Tamerlan when he returned from a trip to Dagestan in July 2012.
Russian authorities had warned the FBI in 2011 about Tsarnaev becoming radicalized. The FBI investigated, and his name was added to a terrorism watch list. But he was still able to fly to Dagestan — an area that has become the center of an Islamic insurgency — spend six months there, and return to the United States.
"There was not sufficient weight put on the information we got from Russia," said U.S. Rep. William Keating, D-Mass., a member of the House Committee on Homeland Security.
A separate report found that Russia was unresponsive when pressed by the FBI for more details.
Three days after the bombings, the FBI released photos of the Tsarnaevs from surveillance video near the bombing sites. Hours later, authorities say, the brothers shot and killed a Massachusetts Institute of Technology police officer in an attempt to steal his gun, then carjacked a Cambridge man.
"'Where's your money?'" carjacking victim Danny Meng said Tamerlan Tsarnaev demanded of him after jumping into his car and showing him a gun.
What Meng thought would be a quick robbery became more terrifying when the man asked him whether he knew about the marathon bombings.
"He said, 'Do you know who did that? I did that.'"
Meng said Tamerlan asked him, "Can your car drive out of state, like to New York?"
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