Remnants of pressure-cooker bomb shown at Boston trial

BOSTON — The Boston Marathon bombing trial jury on Thursday saw the remains of a pressure-cooker bomb that prosecutors say Dzhokhar Tsarnaev hurled at police during a gunfight four days after the bombing as well as jihadist files recovered from his laptop.

The bomb, described as similar to the twin bombs set off at the race, was extracted from a Honda Civic in which it embedded itself on a Watertown, Massachusetts, street after Dzhokhar Tsarnaev and his older brother, Tamerlan, detonated it during the gunfight.

The pressure cooker was the same type as was used in the bombs that killed three people and injured 264 on April 15, 2013, said Federal Bureau of Investigation Special Agent Brian Corcoran, though the pieces found in Watertown were more intact than those discovered at the race’s finish line.

“Those pieces were typically more fragmented, more cut up,” Corcoran testified in U.S. District Court in Boston, looking at both the main pot and its lid, which was found halfway down the block from the blast site, in a child-sized soccer goal in a home’s side yard. “This was a better representation of the pressure cooker as a whole.”

Dzhokhar Tsarnaev, 21, could be sentenced to death if he is convicted of charges that include carrying out the bombing and shooting dead a university police officer three days later as he and Tamerlan, 26, tried to flee Boston.

The Watertown gunfight in the early hours of April 19, 2013, ended when Dzhokhar Tsarnaev hopped into a black Mercedes and attempted to run over three police officers who were trying to arrest Tamerlan. The officers jumped out of the way but Dzhokhar ran over his brother, who was briefly caught up in the vehicle’s wheels and dragged.

Tsarnaev’s lawyers opened the trial early this month by bluntly admitting he carried out the bombing and shooting. Their goal is to convince the jury that the plot was driven by Tamerlan, with Dzhokhar a junior partner in the scheme. Proving that could persuade the jury to sentence the younger brother to life in prison without possibility of parole, rather than death.

Another FBI agent testified that investigators recovered several apparently jihadist documents on Dzhokhar Tsarnaev’s laptop, including at least three copies of Al Qaeda’s “Inspire” magazine, one featuring a cover story headlined “Make a Bomb in the Kitchen of Your Mom,” and another brochure-type document titled “Jihad and the Effects of Intention Upon It.”

The bombing killed restaurant manager Krystle Campbell, 29, graduate student Lingzi Lu, 23, and 8-year-old Martin Richard. Massachusetts Institute of Technology police officer Sean Collier, 27, was shot dead three days later.

Separately on Thursday, Middlesex County District Attorney Marian Ryan said her office would pursue murder charges against Tsarnaev for the shooting of Collier, following his current trial on bombing charges.

Ryan’s office may also soon confirm whether a transit police officer badly wounded during the gunfight was hit by friendly fire. Local media have reported that the officer, Richard Donohue, was wounded after Tamerlan Tsarnaev had run out of bullets in the one working firearm the brothers had.

“The written investigatory report concerning the Laurel Street incident is anticipated to be completed within two months,” Ryan said in a statement. A spokeswoman said the report would include “ballistic information” but declined to confirm whether it would address how Donohue was wounded.

The jury earlier in the trial heard testimony about how Donohue nearly bled to death, though prosecutors asked no specific questions about who had fired the bullet that wounded him.