BOSTON - The Boston marathon bombing suspect has been charged with using and conspiring to use a weapon of mass destruction against persons and property resulting in death.
In the criminal complaint outlining the allegations, investigators said Dzhokhar Tsarnaev and his brother each placed a knapsack containing a bomb in the crowd near the finish line of the 26.2-mile race.
The FBI said surveillance-camera footage showed Dzhokhar manipulating his cellphone and lifting it to his ear just instants before the two blasts.
After the first blast, a block away from Dzhokhar, "virtually every head turns to the east ... and stares in that direction in apparent bewilderment and alarm," the complaint says. Dzhokhar Tsarnaev, "virtually alone of the individuals in front of the restaurant, appears calm."
He then quickly walked away, leaving a knapsack on the ground; about 10 seconds later, a bomb blew up at the spot where he had been standing, the FBI said.
The FBI did not say whether he was using his cellphone to detonate one or both of the bombs or whether he was talking to someone.