Officials say the Massachusetts police officer killed during a traffic stop last weekend was shot in the back.

Auburn Police Officer Ronald Tarentino Jr. was killed early Sunday after stopping an SUV with a license plate not registered to the vehicle.

Chief Andrew Sluckis Jr. said Tuesday the man who shot Tarentino, Jorge Zambrano, got off five shots and Tarentino did not return fire.

Sluckis says one bullet struck Tarentino's body armor, while one .45 caliber bullet entered the space between his gun belt and his bulletproof vest on the lower left of his back.

Zambrano, who had a lengthy criminal record, was shot and killed later Sunday.

Zambrano had several pending criminal cases against him at the time of the shooting, including two for violent encounters with police.