Details emerge about 'pressure cooker' bomb used at Boston Marathon

The two bombs at the Boston Marathon were shrapnel-filled pressure cookers, officials told reporters on Tuesday.

The Associated Press reported the bombs were created by placing explosives and metal objects into 6-liter kitchen pressure cookers. The improvised explosives appear to have been hidden in duffel bags and left on the ground.

The two bombs were placed near the finish line of the Boston Marathon and were about 100 yards apart. They detonated within 10 seconds of each other, killing three people and wounding more than 170 others.

An official told The New York Times that the pressure cookers were filled with nails, ball bearings and black powder. The device was detonated using "kitchen-type" timers.

Similar pressure cooker bombs have been used in Afghanistan, India and Pakistan, according to the Associated Press. Instructions on how to make a pressure cooker bomb were published three years ago in Al Qaeda's English-language magazine Inspire.

The Department of Homeland Security also issued an alert about the bombs in 2004, describing the improvised explosive as a "technique commonly taught in Afghan terrorist training camps."

"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," the alert explained. "As a common cooking utensil, the pressure cooker is often overlooked when searching vehicles, residences or merchandise crossing the U.S. Borders."

A Pakistan-born American citizen who confessed to plotting to detonate a car bomb near Times Square in New York City in 2010 also used a pressure cooker bomb. The device failed to detonate and he was arrested while trying to flee the country.

Despite the link to Al Qaeda and the Taliban, officials have emphasized that anyone was capable of creating the explosive devices. There is currently has no suspect in the bombing and no motive for the attack.