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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.

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Currently the FBI has no suspects or live leads on a suspect or suspects in the case. A Saudi native questioned in a hospital after the attack appears to have been a frightened spectator. An FBI search of an apartment in suburban Revere on Monday evening appears to have produced no connections to the bombing.

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The relatively crude nature of the bombs indicates that it’s likely no sophisticated terror network was involved in the actual attack, according to some experts. The attack points to a “lone wolf” actor who constructed the bomb from instructions readily available on the Internet, including a how-do from Inspire, the English-language magazine of Al Qaeda in the Arabian Peninsula.

Flash powder or an explosive sugar chlorate mixture might have been the bombs' main ingredient, according to an unnamed expert quoted by CNN. That would explain the yellowness of the flame, as shown in video and photos of the event.

Higher-quality military explosive is usually gray or black, said the expert.

Other evidence pointing toward the lone wolf theory includes the fact that no one has yet taken responsibility for the bombing. Organized groups usually do boast about the act – that’s how they spread the “terror” in “terrorism,” after all. But aggrieved individuals, whatever their motivation, are more unpredictable.

Law enforcement officials say it is possible that a lone wolf could be either a domestic terrorist moved by domestic concerns, as was Oklahoma City federal building bomber Timothy McVeigh, or an individual radicalized by Islamist terror teachings. While some aspects of the attack might indicate the latter – two explosions are widely used in Middle East bombings, for instance – the ubiquity of information about bombings means anyone could have picked up such techniques from the Internet with little effort.

Scores of victims of the marathon explosions remain hospitalized. The blast killed 8-year-old Martin Richard after he congratulated his father, who had run in the race. On Tuesday family members identified Krystle Campbell, a young woman from nearby Medford, Mass., as one of the fatalities in the attack. A state-run Chinese newspaper identified the third victim as Lu Lingzi, a Chinese native and graduate student at Boston University.

Boston Police Commissioner Ed Davis said the police presence at the race finish line had been increased for 2013, due to the realization that crowds in the area had grown from past years.

“There was no specific threat about this event,” said Commissioner Davis.

In an indication of the jitters the attack has spread throughout the nation, a United Airlines flight to Chicago returned to the gate Tuesday after passengers became alarmed that two people were speaking a foreign language, the Boston Globe reported. Bags were rescreened before the airliner departed.

[Editor's noteThe original version of this story misspelled Krystle Campbell's first name.]


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