Jurors See Mock-Up Of Pressure Cooker Bomb In Tsarnaev Trial
BOSTON (CBS) - As part of their investigation, FBI experts chose to build mock-ups of every single explosive device connected to the Boston Marathon bombings and the subsequent firefight with police in Watertown.
On Thursday, jurors got to hold and inspect those mock-ups as they heard how investigators literally put the pieces together -- figuring out how transmitters and receivers from radio controlled cars and trucks were used to detonate both finish line bombs.
Boylston Street, prosecutors explained, would be littered with evidence of those devices.
The bombs also had backup fuses, jurors learned. Prosecutors explained that in case the remote controls failed, the pressure cookers could have been lit manually - like a firework - giving the Tsarnaev brothers just seconds to run away.
Prosecutors even showed the receipts for the Tsarnaevs' purchases of the radio controlled components.
When he was asked how difficult it would be for novices to build these bombs, FBI supervisory special agent Ed Knapp said it would be fairly easy, especially with the kind of detailed instructions found in the al Qaeda-sponsored magazines the brothers' had downloaded on their computers. They included step by step plans, and full color photos that are nearly identical to the devices later found at the bombing scenes.
The jury also revisited some of the evidence from the Tsarnaevs' Cambridge apartment - including a strand of Christmas lights. It turns out, jurors heard, that a small bulb from such a strand was used to trigger the connection inside one of the pressure cookers.
The jury also heard that many of the items seized from the Tsarnaev home tested positive for traces of explosive materials, including some kitchen items and some latex gloves found in Tamerlan's car.
The defense team later pointed out that nothing in Dzohkar's dorm contained explosive residue, though there were actual fireworks found there.