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An unnamed FBI official has told CBS Newsthat at least one of the explosive devices detonated in Boston yesterday appears to have been improvised from a conventional pressure-cooker. Unnamed law enforcement officials don’t exactly have the strongest record of credibility in the immediate aftermath of events like these, but federal authorities are well-acquainted with this type of IED.
In mid-2010, the Department of Homeland Security put out a circular, classified “For Official Use Only,” warning of their potential use in domestic attacks:
Rudimentary improvised explosive devices (IEDs) using pressure cookers to contain the initiator, switch, and explosive charge (typically ammonium nitrate or RDX) frequently have been used in Afghanistan, India, Nepal, and Pakistan. Pressure cookers are common in these countries, and their presence probably would not seem out of place or suspicious to passersby or authorities. Because they are less common in the United States, the presence of a pressure cooker in an unusual location such as a building lobby or busy street corner should be treated as suspicious.
The notice (full text below) adds that the failed Times Square bomber used a similar device. And it serves as an update to a 2004 DHS bulletin, also embedded below, citing the existence of such devices in Afghanistan, Pakistan, Nepal, and Malaysia.
Why a pressure cooker? As the DHS alert suggests, it’s a relatively nondescript item, not likely to arouse immediate suspicion to the untrained eye. It can conceal a good deal more explosive and a larger initiating mechanism than, say, a pipe bomb—whose appearance is obvious enough to draw greater scrutiny. Pipe bombs also can’t hold much in the way of shrapnel—nails, BBs, ball bearings—but a pressure cooker makes it easier to carry and conceal such lethal add-ons.
Indeed, these explosives are common enough that some explosive ordnance disposal trainers sell mockup devices to law enforcement. They are familiar to US troops in Afghanistan; the two videos (above and below) are good examples of what a controlled detonation of a pressure-cooker explosive reportedly looks like.
This does not, however, confirm that the Boston bombs have any specific provenance tied to South Asian terrorist or insurgent groups. This might not have come from a group at all: