Marathon Bombs Likely Used Shrapnel, Pressure Cooker, Timer

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:

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.

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:

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

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.