The two bombs that ripped through the crowded final stretch of the Boston Marathon were part of an arsenal of homemade explosives, according to criminal charges made public Monday against the younger of two brothers accused of carrying out the attacks.
The suspects threw explosives from their car as they sought to elude police and left a “low-grade” bomb inside the vehicle they had carjacked at gunpoint, according to the complaint. Authorities described a street strewn with “IEDs” after a shootout with the suspects early Friday. They said they later recovered “a large pyrotechnic” from the surviving brother’s dorm room.
The collection of explosives catalogued in the federal charges suggest that the bombers had assembled far more firepower than they employed in the attacks that killed three and wounded more than 200 along the marathon route on April 15.
Federal, state and local officials have offered conflicting statements on whether the suspects, Tamerlan, 26, and Dzhokhar Tsarnaev, 19, intended to carry out follow-up attacks. The complaint includes no information to suggest that authorities have uncovered evidence that the bombers were eyeing additional targets.
But the charges filed in U.S. District Court in Massachusetts provide the most detailed description so far of the arsenal that the brothers are accused of assembling from widely available materials, including black gunpowder and nails. In all, there were at least eight explosive devices.
Police said shortly after the attacks that the bombs used at the marathon were contained in kitchen pressure cookers, following a recipe available on the Internet, including in an al-Qaeda linked publication known as Inspire.
The FBI affidavit released Monday indicates that authorities recovered the remnants of a nearly identical device, a pressure cooker that “was of the same brand,” at the scene of the shootout in Watertown, Mass., where the older Tsarnaev brother was killed.
The debris could serve as physical evidence to bolster a case that is likely to also rely on extensive video footage from the attacks. Many of the devices were similarly constructed: packed with metal BBs, held together with an adhesive and wired with “green-colored hobby fuse,” according to the affidavit from FBI agent Daniel R. Genck.
The document refers to only a single firearm, used by one of the suspects to carjack an SUV three nights after the marathon. “Did you hear about the Boston explosion? I did that,” the assailant said to the vehicle’s owner, according to the affidavit. The suspect then “removed the magazine from his gun and showed the victim that it had a bullet.”
In a search of the younger Tsarnaev’s dorm room at the University of Massachusetts at Dartmouth, the FBI found a black jacket and white hat “of the same general appearance as those worn by” one of the bombers at the marathon. Agents also recovered “a large pyrotechnic,” according to the complaint. Prosecutors did not describe that device in additional detail.