Prosecutors are using DNA evidence and blood to try and prove that Boston Marathon bomber Dzhokhar Tsarnaev (joh-HAHR' tsahr-NEYE'-ehv) and his brother both played prominent roles in the 2013 attacks and the killing of a Massachusetts Institute of Technology police officer.

A DNA expert testified Wednesday that Officer Sean Collier's blood 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 say the brothers fled the scene of Collier's shooting in the Honda.

During cross-examination, Tsarnaev's lawyers established that Tsarnaev didn't have Collier's blood on the sweatshirt he wore that night.

Testimony resumes Thursday.