Federal authorities continue to investigate Boston Marathon bombing


POSTED: Wednesday, April 17, 2013 - 7:57am

UPDATED: Wednesday, April 17, 2013 - 8:20am

Police and federal agents say they have no suspects in the Boston Marathon bombing, but they are beginning to assemble the bits of evidence they'll need to solve the case.

The first question has now been answered, how many explosive devices were actually left at the scene? That answer is two, and officials describe them as crudely made, but effectively used, NBC's Pete Williams reports.

Investigators have begun the process of recovering tiny pieces of the bombs to learn how they were made. They say it appears the devices were assembled inside pressure cooker pots packed with BB's and ball bearings and nails to magnify the injury.

As these Homeland Security bulletins note, pressure cookers have been used for decades in terror bombings. Instructions for making them appear on the Internet, including just last month in Al Qaeda's online magazine, "Inspire".

Investigators say the explosive in Boston was most likely smokeless powder, gunpowder, available at sporting goods stores, not something more powerful like dynamite. They believe the bombs were carried to the scene in dark nylon bags and set off by timers.

A former bomb investigator says the experts know what to look for, "They're able to recognize the minute pieces of an article that a civilian wouldn't even know what it was, but to a bomb investigator, like ATF or FBI, will say, that's from a clock, that's from a battery."

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