The recipe is straightforward. First you take a small quantity of explosives made from cleaning fluid and place it in a pressure cooker with a liberal helping of small metal objects, such as ball bearings or nails. Then fit an everyday electronic device, such as a digital watch or a mobile phone, to trigger the apparatus, and hey presto, you've built a homemade bomb with truly devastating firepower.
The FBI and other American intelligence agencies are still poring over the wreckage of this week's Boston marathon.
What is clear, though, is that those responsible for this outrage relied on cheap, easy-to-build and devastatingly effective devices to carry out the attack, which killed three people and caused dozens more to suffer traumatic injuries. The shredded remnants of domestic pressure cookers that have been recovered close to the blast site bear all the hallmarks of the improvised explosive devices that have recently had a dramatic increase in popularity among a wide variety of terrorist organisations.
Pressure cookers are particularly favoured by modern terrorists because their thick metal casing produces large quantities of shrapnel that inflicts the maximum amount of damage to victims. Their use in the Boston bombings would explain the high number of amputations carried out on the wounded.
Thanks to the efforts of jihadist and anarchist groups, the basic instructions for assembling one of these crude devices are now freely available on the internet. Inspire, the internet-based jihadi magazine published by the American-born radical cleric Anwar al-Awlaki, famously published a feature entitled "Make a Bomb in the Kitchen of your Mom", which provided detailed information about what kind of explosives to use, and how to choose the most appropriate detonator. In many respects, the article was little different to similar pieces that were published by anti-government activists in the 70s, such at The Anarchist Cookbook, by the anti-Vietnam War campaigner William Powell, which contained instructions on the manufacture of basic explosives. During the Troubles in Northern Ireland, the IRA also regularly produced pamphlets instructing its supporters on bomb-making techniques.
But the ready availability of such material online during the past decade means expertise once confined to extremists can be accessed by anyone bearing a grudge.
The neo-Nazi activist responsible for bombing a packed gay pub in Soho relied on a homemade device, as did the al-Qaeda sympathisers responsible for the July 7 bombings in London in 2005.
Thanks to the internet, primitive explosive devices that were developed by insurgent groups fighting in Iraq and Afghanistan are now just as likely to be used in American and European cities as they are on the streets of Kabul and Baghdad. On the day of the Boston marathon attack, 50 people were killed by similar devices used in an al-Qaeda-orchestrated wave of explosions in the Iraqi capital.
The ease with which people can learn to make homemade explosives adds to the burden of intelligence security services.
Enormous strides have been made on both sides of the Atlantic in the ability of security specialists to identify and disrupt potential terror cells. The four British al-Qaeda sympathisers given lengthy prison sentences yesterday for their plot to use a remote-controlled toy car to attack the Territorial Army headquarters in Luton were apprehended following a lengthy MI5 surveillance operation that taped their discussions about building a homemade device. Indeed, the reason Britain has not suffered a major terrorist incident since the July 7 attacks is primarily due to the increased effectiveness of the security service's monitoring of potential cells. But keeping tabs on the activities of lone individuals who might be planning some diabolical attack is more problematic.
As Sir Jonathan Evans, MI5's recently retired chief, remarked during a rare public speech last year: "There is no shortage of individuals talking about wanting to mount terrorist attacks here." The same, apparently, is true in America, where, while security officials were investigating the Boston bombings, there was an unrelated attempt to poison President Obama with ricin. This was thwarted by alert security officers.
It was a full 24 hours after the Boston bombings before the President denounced them as "acts of terrorism". Those responsible for this week's attacks may be amateurs, but when they get the formula right, the consequences can be devastating. And denouncing their actions as acts of terrorism is the only way to describe this terrible evil.
- Telegraph Group Ltd