FBI Special Agent Richard DesLauriers said in a news conference Tuesday that investigators have recovered fragments of black nylon, BBs and nails at the scene of the Boston marathon explosions.
"Among items partially recovered are pieces of black nylon, which could be from a backpack, and what appear to be fragments of BBs and nails, possibly contained in a pressure cooker device," he told reporters. "We are expediting this blast evidence to our laboratory in Quantico, Virginia, for a complete and thorough analysis.
"In addition, this morning it was determined that both of the explosives were placed in a dark colored nylon bag or backpack. The bag would have been heavy because of the components believed to be in it. At this point, it is difficult to determine specific components used until we can eliminate other factors which may have already been present in the environment. In fact, we won't know with some certainty until the laboratory completes its final review."