Along with determining that the suspects had made at least five pipe bombs, the authorities recovered four firearms that they believe the suspects used, according to a law enforcement official. The authorities found an M-4 carbine rifle — a weapon similar to ones used by American forces in Afghanistan — on the boat where the younger suspect was found Friday night in Watertown, Mass., 10 miles west of Boston.
Two handguns and a BB gun that the authorities believe the brothers used in an earlier shootout with officers in Watertown were also recovered, said one official briefed on the investigation. The authorities said they believe the suspects had fired roughly 80 rounds in that shootout, in which Tamerlan Tsarnaev was fatally wounded, the official said.