[The following are excerpts from an article headlined FBI unit zeroing in on design of devices published today on the website of The Boston Globe:]
FBI bomb technicians poring over hundreds of scraps of metal, nails, wires, and other debris — some surgically removed from bomb victims’ flesh — were closing in Thursday on the design of the explosive devices used in the Boston Marathon attacks, according to officials and forensics experts.
In an effort to trace the source of the components, the Explosives Unit at the agency’s state-of-the-art crime laboratory in Quantico, Va, outside of Washington, was comparing the materials collected from sidewalks, rooftops, gutters, overhangs, and even the soles of victims’ shoes against lab reports generated from thousands of previous blasts around the world, looking for a “bomber signature.” (...)
The methodical work at Quantico is seen as critical in helping investigators identify the perpetrators and secure a conviction in the worst terrorist attack on US soil since Sept 11, 2001.
“Most bombing investigations like this are forensically driven,” said former supervisory special agent James T Thurman, who served as chief of the Explosives Unit in the FBI Laboratory’s Bomb Data Center. “Whatever is found that ultimately goes to the laboratory is what drives the investigation and connects a possible subject with the components.” (...)
[T]hose familiar with the inquiry and the FBI’s lab said the Explosives Unit is relying on specialized tools to conduct what amounts to an autopsy on the pair of so-called IEDs — improvised explosive devices — that were apparently detonated by battery-powered timers near the Copley Square finish line.
One is a database known as the Explosive Reference Tool, a searchable computer archive containing investigation reports from bombings dating back decades, along with so-called underground bomb-making handbooks and manufacturing data for key bomb-making components and explosives. (...)
Potential evidence that was identified, bagged, and tagged — including by agents who spread out to hospitals to secure bomb material and residue removed from wounds — began arriving in the Quantico lab even before the bombing sites were fully swept for evidence.
“It is a two-way street,” said Thurman, who investigated the bombings of the US Marine Corps barracks in Lebanon in 1983, Pan Am Flight 103 in 1988, and World Trade Center in 1993. He explained that as the lab uncovers clues and materials it may send orders back to the bombing scene to look for specific things.
“They will continue that as long as it takes,” he added. “It can take less than a day. It can take a week. It can take two weeks.”
Thurman, who teaches at Eastern Kentucky University, also cautioned that it could take longer, citing the bombing of a judge in Alabama in 1988, when the forensics analysis took two years.
“This is not an overnight thing,” he said. “The issue at the end of the day is to find the guilty party who is responsible for constructing and setting off these devices,” he said. “You are ensuring that the right people and not the wrong people are being charged.”
[Tom Thurman’s part in identifying the dodgy timer circuit board fragment in the Lockerbie investigation is dealt with here and here.]