Investigators work near the location where the previous night a suspect in the Boston Marathon bombings was arrested, Saturday, April 20, 2013, in Watertown, Mass. Police captured Dzhokhar Tsarnaev, 19, the surviving Boston Marathon bombing suspect, in a backyard boat after a wild car chase and gun battle earlier in the day left his older brother dead. (AP Photo/Matt Rourke)
BOSTON (AP) -- The criminal complaint that charges Dzhokhar Tsarnaev (joh-KHAR'tsahr-NEYE'-ehv) in last week's Boston Marathon bombing sheds no light on a motive for the attack.
But it does include some additional details about the activities of Tsarnaev and his older brother, who would later be killed after a shootout with police.
The FBI says Tsarnaev was seen on surveillance cameras putting a knapsack down on the ground near the site of the second blast, and then manipulating a cellphone and lifting it to his ear. Seconds later, the first explosion went off a block away -- and Tsarnaev, unlike nearly everyone around him, appeared calm, and quickly walked away. According to the court papers, the second blast occurred 10 seconds later, where he had left the knapsack.
The FBI didn't make it clear whether it thought he had used the phone to detonate one or both of the bombs.
The court papers also said that during the Thursday night violence that led to the death of the older brother and the capture of Tsarnaev, one of them had told a carjacking victim that he had carried out the bombing.
In the complaint, the FBI also says it searched Tsarnaev's dorm room Sunday and found BBs, as well as a white hat and dark jacket that looked like the ones won by one of the suspected bombers.