This Homeland Security Department pamphlet, from July 2010, distributed to police, fore, EMS and security personnel shows a diagram for rudimentary improvised explosive devices (IEDs) using pressure cookers to contain the initiator, switch and explosive charge. A person briefed on the Boston Marathon investigation says the explosives were in 6-liter pressure cookers and placed in black duffel bags. (AP Photo/Homeland Security Department)

Associated Press
This Homeland Security Department pamphlet, from July 2010, distributed to police, fore, EMS and security personnel shows a diagram for rudimentary improvised explosive devices (IEDs) using pressure cookers to contain the initiator, switch and explosive charge. A person briefed on the Boston Marathon investigation says the explosives were in 6-liter pressure cookers and placed in black duffel bags. (AP Photo/Homeland Security Department)
This Homeland Security Department pamphlet, from July 2010, distributed to police, fore, EMS and security personnel shows a diagram for rudimentary improvised explosive devices (IEDs) using pressure cookers to contain the initiator, switch and explosive charge. A person briefed on the Boston Marathon investigation says the explosives were in 6-liter pressure cookers and placed in black duffel bags. (AP Photo/Homeland Security Department)
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