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Boston Marathon bombing: '6L' mark, circuit boards may be key clues (+video)

Investigators have scoured the crime scene of the Boston Marathon bombing for every possible physical clue. A crucial task is to collect as many bomb fragments as possible, to track where the parts came from and who bought such items.

By Staff writer / April 17, 2013

People have been placing flowers and remembrances for victims of the Boston Marathon bombing at a roadblock manned by National Guardsmen at the end of Boylston Street, on Wednesday, in Boston, Massachusetts.

Melanie Stetson Freeman/The Christian Science Monitor


Federal agents are quickly determining how the Boston Marathon bombing was carried out, but the question of who is responsible remains a mystery as the investigation into the deadly attack scours a massive crime scene for answers.

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Under the direction of the FBI, more than 1,000 law enforcement officers are going over every inch of a large portion of Boston’s Back Bay in an effort to find every scrap that might possibly represent a physical clue, said FBI Special Agent in Charge Richard DesLauriers at a Tuesday evening briefing. They’re interviewing every eye witness they can find and matching evidence with existing law enforcement databases.

Both of the bombs were packed in heavy, dark bags, probably duffel bags or backpacks, said Mr. DesLauriers. He asked anyone who had seen a person struggling with such a load near the marathon's finish line on April 15, or anyone who had heard a friend, relative, neighbor, or coworker talk about targeting the iconic race in any way, to call the FBI.

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

Two blasts ripped through the Back Bay crowd seconds apart on Monday just before 3 p.m. Early indications are that the bombs had a basic explosive element, such as gunpowder or residue from match heads, placed inside common pressure cookers. Nails or ball bearings were added to create shrapnel.

Pictures from a law enforcement bulletin obtained by the Associated Press and Reuters showed pictures of mangled pressure cooker scraps, scraps of black nylon, a circuit board, and a battery with wires attached.

DesLauriers declined to speak publicly about this evidence. But news reports indicate that the FBI believes it may have recovered enough physical remains of the bombs to start the crucial business of reconstructing where parts came from and how they were assembled.

According to The New York Times, one of the pressure cooker scraps is inscribed “6L,” for six-liter capacity. The Spanish company Fagor is one firm that makes cookers identified with such a stamp. It sells 50,000 of them in the US every year, the Times reported.

At least some of the nails in the bombs were tiny, the size of picture-hanging nails or brads, according to NBC News.

A witness has provided WHDH, an NBC affiliate in Boston, with two photos that may help determine where and how one bomb was positioned, among other things.

The first photo shows a dark bag next to a mailbox and barricade along the marathon route. The second shows no bag, and injured people and debris blown about the scene.

“A man took the images from his office above Boylston Street and they show the moments right after one of the explosions,” wrote WHDH reporter Susan Tran.


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Danny Bent poses at the starting line of the Boston Marathon in Hopkinton, Mass.

After the Boston Marathon bombings, Danny Bent took on a cross-country challenge

The athlete-adventurer co-founded a relay run called One Run for Boston that started in Los Angeles and ended at the marathon finish line to raise funds for victims.

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