The shooting occurred at 1:03 p.m. at the Park Sierra Apartments at 6450 Dougherty Road.
Alameda County sheriff's Sgt. J.D. Nelson told reporters at the scene this afternoon that the officers were searching the apartment of a suspect who had committed various crimes, including robberies.
During the search, one of the BART officers was shot, and it appears he was shot accidentally by another BART officer at the scene, Nelson said.
The wounded officer was taken to Eden Medical Center in Castro Valley, where he succumbed to his injuries, Nelson said.
Nelson said there are no suspects at large, and Dublin police are investigating the shooting. The city of Dublin contracts with the sheriff's office for police services.
BART Police Chief Kenton Rainey and General Manager Grace Crunican said in a statement, "The entire BART organization is deeply saddened by this tragic event and we ask the public to keep the officer's family in its thoughts and prayers."