Prosecutors use blood, DNA to show bomber's active role

BOSTON (AP) - Prosecutors presented DNA and blood to try showing that Boston Marathon bomber Dzhokhar Tsarnaev and his brother both played prominent roles in the 2013 attacks and the killing of a Massachusetts Institute of Technology police officer days later.

A DNA expert testified Wednesday that the blood of Officer Sean Collier appeared on white gloves found in Tsarnaev's car.

Jennifer Montgomery, a DNA analyst with the state police crime lab, said Collier's blood was on a pair of gloves found near the gas pedal and driver's seat of Tsarnaev's Honda Civic. Prosecutors have said the brothers fled the scene of Collier's shooting in the vehicle.

But during cross-examination, Tsarnaev's lawyers established that none of the blood found on the sweatshirt Dzhokhar wore that night was Collier's. The analyst said it was all Dzhokhar's blood.

An MIT graduate student testified earlier that he saw Tsarnaev leaning into Collier's cruiser the night he was killed. Collier was shot six times, including three times in the head at close range. Tsarnaev's lawyers apparently were trying to suggest that he would have had Collier's blood on his sweatshirt if he had fired the gun.

After Collier's killing, the Tsarnaevs had a shootout with police in Watertown. Older brother Tamerlan died following the gunfight and being run over by Dzhokhar as he fled. Dzhokhar was found hours later wounded and hiding in a boat parked in a backyard.

Tsarnaev, 21, faces the possibility of the death penalty for his role in the April 15, 2013 bombings. Three people were killed and more than 260 were injured when two pressure-cooker bombs exploded near the marathon's finish line.

Tsarnaev's lawyer admitted during opening statements that he participated in the bombings but said Tamerlan was the mastermind. His lawyer also said it was Tamerlan, not Dzhokhar, who shot Collier.

Testimony is scheduled to resume Thursday.