The FBI is now saying that pressure cookers were used to create the explosive devices used in the Boston Marathon Bombings. What is a pressure cooker and how can it be used to make a bomb?

Scraps of black, sturdy nylon material found at the explosion sites are now leading investigators to speculate that the explosives were likely transported in heavy, dark-colored duffel bags.  Ball bearings, or possibly BB bullets, and nails were also used, packed inside what appear to be pressure cookers.

There are still many details that have yet to be discovered and released, but for many the question is, "How can a pressure cooker be used to make an explosive?"

The use of pressure cookers to make explosives is not new.  In fact, in 2004 the United States Department of Homeland Security issued a warning about their use by terrorists, citing real-life examples from as early as 2001.

According to the statement, explosives are put inside the pressure cooker and the manufactured device can then be activated using items ranging from a garage door opener to a cellular telephone.  And excerpt from the DHS Information Bulletin warning appears below:

United States Department of Homeland Security

Homeland Security also posted photos of commonly-used pressure cookers.  Hopefully, the dissemination of this information qualifies as an "official use."

Department of Homeland Security Information Bulletin

Another warning, issued on July 1, 2010, by Homeland Security and the Federal Bureau of Investigation, warned against "rudimentary improvised explosive devices" used in attacks in 2010 - one in March in Pakistan and another on May first in New York's Times Square.

More than 180 people are now said to have been injured in the bombings which killed three people on Monday, April 15, 2013.