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?”
A week later, former New York Police Commissioner Raymond Kelly said Dzhokhar Tsarnaev told investigators from his hospital bed that he and his brother decided that night to drive to New York City and launch a second attack.
Meng escaped by running when the Tsarnaevs stopped at a gas station. Authorities said the brothers drove to nearby Watertown, where a wild gun battle with police erupted on a quiet side street, with the brothers shooting at officers and throwing three pipe bombs and one pressure cooker bomb.