Boston: whoever did it knows how Taliban make their bombs

THE ONLY solid information on the Boston Marathon bomb attack that the FBI and President Obama's White House security apparatus could offer last night was on the bombs themselves: they were made by packing 6-litre pressure–cookers with ball-bearings, nails and explosives.

But this only adds to the deepening mystery of who planted the bombs and why, writes Charles Laurence from New York. On the one hand, pressure-cooker bombs are on the syllabus in terror training camps in Afghanistan and Pakistan. On the other, the simplicity of the devices that killed three and injured more than 170 points to "domestic terrorism", or even a lone mass-murderer.

There has been no claim of responsibility.

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President Obama, in a second address within 24 hours, stressed that no one yet had any idea whether an organisation - either domestic or foreign - or a "malevolent individual" was responsible, or what the motive might have been.

"Everything else at this point is speculation," he said.

By last night, the FBI had gathered enough fragments from the gore at the two bomb sites near the marathon finish line to know that the pressure-cookers – sealed stove-top containers used for fast cooking or preserving of food – had identical '6L' markings on them, and that they had been filled with ball-bearings, nails and air-gun pellets to create crude but devastating shrapnel bombs.

They were probably powered by explosives made from over-the-counter fertilisers and set-off with a detonator. That would match the ratio of smoke to 'bang'. Another report suggested a 'black powder' mixture was used - as legally available through gun shops in America as a military rifle.

The bombs had been left in black nylon duffle bags or back packs, perhaps in litter bins – an old IRA trick in the 1970s, leading to their general removal from central London streets and Underground stations. But these bags were more probably left on the ground, offering a trajectory that explains the horrific leg injuries and the death of eight-year-old Martin Richard.

CNN carried a report that a video of a bag on the ground next to a mail box seemed to match a video of one of the bombs going off.

The FBI has fragments of circuit-boards, too. They indicate that the bombs were triggered by a timing device, rather than a signal from a mobile phone. The New York Times quoted a policeman as saying the circuits may been adapted from egg-timers.

Not surprisingly, the FBI is appealing for any shopkeepers who have recently sold pressure-cookers, egg-timers or over-the-counter chemicals to get in touch. They also want every photo and video taken at the marathon they can get hold of, and there must be tens of thousands of those. They plan to scan them against passport photos, diving licence records, visa, and records kept from every passenger through a US border.

FBI 'profilers', the experts used to conjure identities of serial killers, are working up theories on anyone from home-grown jihadi to an ice-cream salesman with a grudge over a concession, who might want to hit the Boston Marathon.

Special Agent Rick DesLauriers, in charge of the FBI's Boston office, also asked people to report anyone who talked about targeting Monday's race or showed interest in explosives. He urged anyone who might have heard the sounds of explosions in remote areas in recent days - made by someone testing a bomb - or saw someone on Monday carrying "an unusually heavy, dark-coloured bag" to come forward.

"Someone knows who did this," said DesLauriers. "Cooperation from the community will play a crucial role in this investigation."

Jeff Beatty, who has served with both the FBI and CIA, told CNN that Taliban and al-Qaeda militants use pressure-cookers to make their IEDs (improvised explosive devices). "But that doesn't mean it was the Taliban," he said. "Other people can read about this."

As The Week reported yesterday, there are as many signs pointing to a "domestic terrorism" as there are to foreign radicals.

In Washington yesterday, Sen. Saxby Chambliss, the senior Republican on the Senate Intelligence Committee, told reporters that some of the facts they had been given in a briefing from Homeland Security suggested the attack was "domestic".

"There are a lot of things that are surrounding this that would give an indication that it may have been a domestic terrorist," Chambliss said, "but that just can't be assumed."

On Thursday, Obama flies to Boston to speak at an interfaith church service to commemorate the victims. His security apparatus is sending out signals that there is no evidence that the Boston bombing is the harbinger of more terror to come, or that there are any other signals of threat.

He has - as he must - pledged that the killer or killers will be brought to justice. But it is dawning on Americans that, in this strange case, that could take some time.