(AP) — A person briefed on the Boston Marathon investigation says the explosives were in 6-liter pressure cookers and placed in black duffel bags.
The person says the explosives were placed on the ground and contained shards of metal, nails and ball bearings. The person spoke on the condition of anonymity because the investigation was ongoing.
The person says law enforcement officials have some of the bomb components but did not yet know what was used to set off the explosives.
President Barack Obama said Tuesday the bombings were an act of terrorism but investigators do not know if they were carried out by an international or domestic organization, or perhaps by a “malevolent individual.”
While the devices have been frequently used in Afghanistan, India and Pakistan, in recent years they have also shown up in plots in the U.S. and France.
Explosives typically are placed inside a pressure cooker — a commonplace cooking utensil in many countries — and the device is then detonated using everyday electronic equipment such as digital watches, garage door openers, cellphones or pagers. Pressure builds inside the container and shrapnel is expelled. Al-Qaida affiliates have provided training and manuals on how to build such devices.
Here’s a look at some of the most recent container bombs:
February 2013: A bomb hidden in a pressure cooker explodes inside a restaurant in northern Afghanistan, killing five people.
October 2012: French police find bomb-making materials in an underground parking lot near Paris as part of a probe into an attack on a kosher grocery. The discovery includes bags of potassium nitrate, sulfur, headlight bulbs and a container used as a make-shift pressure cooker.
May 2012: U.S. jurors hear that explosives experts had found a pressure cooker containing smokeless gunpowder and other material in the Texas motel room of a soldier accused of planning to blow up Fort Hood military troops and other personnel.
May 2010: One of the three devices used in the May 2010 Times Square attempted bombing was a pressure cooker, according to a joint FBI and Homeland Security intelligence report issued in July 2010.
March 2010: Suspected militants attack the U.S.-based Christian aid group World Vision in northwestern Pakistan, killing six Pakistani employees. Officials say the attackers remotely detonated a pressure cooker bomb.
March 2006: A series of bombings kill 20 people in India. One bomb — at a temple in the northern city of Varanasi where five people died — was placed in a pressure cooker and detonated by a timing device.
December 2004: Ten accused Islamic militants are convicted for their roles in a plot to blow up a Christmas market in the eastern French city of Strasbourg on New Year’s Eve 2000. Authorities say the group had planned to blow up containers packed with explosives, a technique they allegedly learned in Afghan camps.
August 2002: Explosives packed in a pressure cooker shake a shopping mall in Katmandu, the capital of Nepal. Shops are damaged but there are no casualties.