The Associated Press has reported that the explosives used to bomb the Boston Marathon on Monday were homemade pressure cooker devices.
A person who spoke on the condition of anonymity because the investigation was still going on said that the explosives were put in 6-liter pressure cookers, placed in black duffel bags and left on the ground. They were packed with shrapnel, the person said.
The devices are apparently very easy to make, as one simply loads explosives into the pressure cooker and adds a blasting cap to the top. The Department of Homeland Security issued a warning about terrorist pressure cooker bombs back in 2004.
Typically, these bombs are made by placing TNT or other explosives in a pressure cooker and attaching a blasting cap at the top of the pressure cooker. The size of the blast depends on the size of the pressure cooker and the amount of explosive placed inside. Pressure cooker bombs are made with readily available materials and can be as simple or as complex as the builder decides. These types of devices can be initiated using simple electronic components including, but not limited to, digital watches, garage door openers, cell phones or pagers. As a common cooking utensil, the pressure cooker is often overlooked when searching vehicles, residences or merchandise crossing the U.S. Borders. [Washington Post]