Firework gunpowder and toy remote set off bombs
The bombs that tore through the crowd at the Boston Marathon were sparked by a remote control from a toy car and powered by flash powder from fireworks, FBI experts have said.
Federal Bureau of Investigation chemistry specialist David McCollam testified in the 14th day of Dzhokhar Tsarnaev's trial on charges of killing three people and injuring 264 people with a pair of homemade pressure-cooker bombs at the race's finish line on April 15, 2013.
The bombs used in the attack, as well as others thrown at police during a gunfight in the suburb of Watertown, Massachusetts, after Tsarnaev and his older brother, Tamerlan, allegedly killed a university police officer, had the distinctive signs of low-powered explosives, said McCollam.
Prosecutors contend the bombs were stuffed with gunpowder taken from commercial fireworks and shrapnel.
The jury yesterday saw a photo of an intact 'Big Snow' firework found in Dzhokhar Tsarnaev's dorm room at the University of Massachusetts at Dartmouth and another, with the powder removed, found in a backpack taken from the room by a friend of Tsarnaev.
"There's a lot of effort that would go into separating out the pyrotechnic or firework explosive," McCollam said.
Small bulbs from a set of Christmas tree lights, wired to a controller cannibalised from a remote-control car, were used to set off the bombs, said Edward Knapp, an FBI supervisory special agent who reconstructed the bombs used in the attack.
Fuses also appeared to have been installed in both bombs as a backup ignition method, he added.
Tsarnaev (21) could be sentenced to death if he is convicted by the US District Court jury in Boston. Tamerlan (26) died four days after the bombing of injuries sustained during the gunfight, which ended when Dzhokhar sped off in a hijacked SUV, running over Tamerlan in the process.
Dzhokhar Tsarnaev briefly escaped, prompting a day-long lockdown of most of the greater Boston area while police conducted a massive manhunt. He was found hiding in a boat parked in a backyard late on April 19, 2013.
Tsarnaev's lawyers opened the trial early this month with a blunt admission that their client committed all the crimes of which he is accused. Rather than trying to prove his innocence, they are trying to avert a death sentence by convincing the jury that Tamerlan was the driving force behind the attacks.
The same jury that determines whether Tsarnaev is guilty will decide whether he is sentenced to life in prison without the possibility of parole, or death.
The bombing killed restaurant manager Krystle Campbell (29), graduate student Lingzi Lu (23), and 8-year-old Martin Richard.
Tsarnaev is also charged with the fatal shooting of Massachusetts police officer Sean Collier three days after the bombing.