The April 15 bombing, using pressure cookers packed with explosives, nails, ball bearings and metal shards near the marathon's finish line, killed three people and injured more than 260 others. Authorities said Tsarnaev and his younger brother later killed a Massachusetts Institute of Technology campus police officer and carjacked a driver, who later escaped.
Authorities said that during the gunbattle with police, the Tsarnaev brothers, ethnic Chechens from Russia who came to the United States about a decade ago, set off another pressure cooker bomb and tossed grenades before the older brother ran out of ammunition.
Police said they tackled the older brother and began to handcuff him but had to dive out of the way at the last second when the younger brother, 19-year-old Dzhokhar Tsarnaev, drove a stolen car at them. They said the younger brother ran over his brother's body as he drove away from the scene to escape.
Dzhokhar Tsarnaev was captured later, wounded and bloody, hiding in a tarp-covered boat in a suburban Boston backyard. He is in a federal prison and faces a charge of using a weapon of mass destruction to kill.
The Tsarnaev brothers' mother insists the allegations against them are lies.
Three of Dzhokhar Tsarnaev's friends, college classmates, were arrested Wednesday and accused of helping after the marathon bombing to remove a laptop and backpack from his dormitory room before the FBI searched it.
A top Republican senator on Thursday asked President Barack Obama's administration to explain how one of the students entered the United States without a valid student visa.
Sen. Chuck Grassley, of Iowa, in a three-page letter to Department of Homeland Security Secretary Janet Napolitano, asked for additional details about the student visa applications for Azamat Tazhayakov and Dias Kadyrbayev, college roommates from Kazakhstan charged with obstruction of justice in the marathon bombing case, and how Tazhayakov was allowed to re-enter the United States in January.