REVERE, Mass. -- Authorities said Tuesday morning they have made arrests in connection with the shooting of an off-duty Revere police officer last weekend.

They would not release further details but were expected to have more information later in the morning.

The Suffolk district attorney said the police officer, Daniel Talbot, who was killed Saturday in a shootout with a group of young men, was not shot by a fellow officer.

Talbot was shot once in the head early Saturday morning as he socialized with other off-duty officers in a parking lot behind Revere High School.

District Attorney Daniel Conley said there was some kind of confrontation and an unidentified shooter fired on the officers, who fired back.

Conley said an autopsy report shows the bullet that killed Talbot was not the same caliber as weapons the other officers carried.

The 30-year-old Talbot was a five-year veteran of the force who was assigned to the gang unit. Conley said it's not clear if the men who confronted the officers were gang members.