The Boston Marathon bombing is only the second time that a pressure cooker is being used as a terror bomb in the United States. But this type of bomb is common terror and insurgency weapon in West and South Asia.
The most obvious reason is that pressure cookers are rarities in Western kitchens. “This is not a device that Americans are familiar with,” says Ajai Sahni of the South Asia Counterterrorism Portal.
This has led analysts to ask whether there is an international connection to the Boston bombing going back to the Arab world or the subcontinent.
After all, the only previous use of a pressure cooker terror weapon in the US was by the Pakistan Taliban-trained Times Square bomber.
However, there are at least three ways that a US bomber could have learnt about how to make a pressure cooker bomber.
One is the internet.
The Al Qaeda e-magazine Inspire ran a few articles on how to make bombs from “your mama’s kitchen” that included using a pressure cooker.
Two is Afghanistan and Iraq where hundreds of thousands of US soldiers served and had to face insurgents who used such bombs.
This is one reason the Boston bomber being a rightwing American extremist is still not being completely ruled out.
Three, of course, is the bomber having some connection with terrorist groups in South Asia, as was the case with Faisal Shehzad, the Times Square terrorist.
In India, pressure cooker bombs have been widely used by the Indian Mujahideen. Use of this weapon in Pakistan began widespread after 9/11, though they were introduced there from the fighting in Afghanistan in the 1970s and 1980s.
Indian officials see South Asian hallmarks in the attack. “Targeting an event such as the annual marathon rather than a place or landmark was very South Asian. There attacks are around events such as Diwali, Holi or Muharram.”
But US terrorism experts like Bruce Riedel are circumspect. “The pressure cooker device is very simple and has been used around the world,” says the Brookings scholar.
So far, US intelligence and counterterrorism agencies have not approached the Indian system for any assistance, say senior Indian officials.