FBI toggle caption FBI The explosive devices were made from galvanized steel pipes and had plastic kitchen timers mounted on top. FBI The explosive devices the suspect made were rather generic: simple bombs made from 1-by-8-inch galvanized steel pipes — the kind plumbers use — with plastic kitchen timers mounted on top, the ones you spin around to set. The FBI said the explosive inside was homemade black powder, which can be a mix of just about anything that will ignite; typically it includes saltpeter, sulfur and gunpowder. "What I think would be accurate to say, given the information we have, is this is a very hazardous device that could kill people," said Barry Black, a retired FBI special agent and master bomb technician who helped investigate the 1995 Oklahoma City bombing.