BOSTON — The FBI says in an affidavit that the Boston Marathon bombing suspect was seen using a cellphone after placing a knapsack on the ground at an explosion site.

The document does not say whether suspect Dzhokhar Tsarnaev is thought to have used the cellphone as a detonator.

The affidavit also says one of the bombers told a carjacking victim, “Did you hear about the Boston explosion? I did that.”

It says Tsarnaev had apparent gunshot wounds to the head, neck, legs, and hand when he was brought to a hospital after his capture Friday.