NEW YORK (AP) _ A transit worker went on a rampage in a subway power shed Friday, shooting and killing a co-worker and wounding his supervisor before killing himself.

Investigators were not sure what set off the shooting in the train yard in the city's borough of the Bronx, where the worker opened fire with a .38 caliber handgun, said Deputy Chief George Latimer of the transit police.

A co-worker, Richard Charles, died from one gunshot behind the left ear, said Latimer. Supervisor August Muschitiello, 35, was treated at a hospital for gunshots to the chest and leg.

Police said the gunman, John O'Brien, 37, shot himself twice in the chest and was dead when officers arrived. Authorities were summoned by a college student who was walking in the area and heard the shooting.

O'Brien also carried a plastic bag with 10 more rounds of ammunition, authorities said.

The shooting occurred just south of the last stop on a subway line that runs underneath Manhattan and above ground through the Bronx, authorities said.