Marathon Bombs Likely Used Shrapnel, Pressure Cooker, Timer

A few details about the bombs that exploded during the Boston Marathon on Monday are starting to emerge.

Here's what we know so far about the two bombs that killed three and injured more than 100 others:

The two bombs were reportedly transferred in backpacks and stuffed into trash cans, so the explosives had to be simple, small, and powerful.

The vice president of intelligence company Stratfor had this to say:

#Boston IEDs were probably crude, black powder in composition.

— Fred Burton (@fred_burton) April 16, 2013

The LA Times quotes officials as saying that the explosives were not made of plastic, which would have caused a much greater shock wave.

There were also several reports of ball bearings zipping around, peppering victims.

RT @globecynthia: Brigham doctor now saying they removed ball bearings and nails from patients. MGH Doc said the same a little while ago.

— The Boston Globe (@BostonGlobe) April 16, 2013

Again, this is a common tactic with suicide and smaller bomb varieties, to duct tape or otherwise affix bags of screws and ball bearings to the outside of the explosive.

There are other ways to achieve the type of shrapnel needed to hurt and maim victims:

Source tells @cbsnews one of the explosive devices--the one found near the Starbucks--appears to have been placed in a metal pressure cooker

— Charlie Kaye (@CharlieKayeCBS) April 16, 2013

Also, authorities are saying at least one of the bombs "likely" had a timing device attached:

Official: "Likely but not certain" timer was attached to explosive in Boston. on.cnn.com/13b4FmV

— CNN Breaking News (@cnnbrk) April 16, 2013

On the other hand, authorities have told ABC that the bombs could have also been remotely detonated, possibly via cell phone. Using this method, a bomber would attach a cellphone to the bomb's circuitry so the bomber would just have to dial a number to set it off.