SAN FRANCISCO -- A Bay Area Rapid Transit police officer was accidentally shot and killed by a partner Tuesday while conducting a probation search at a Dublin apartment complex, authorities said.

Alameda County Sheriff's Department Sgt. J.D. Nelson, a spokesman, said the incident occurred about 2 p.m. at the sprawling Park Sierra Apartments, in the 6400 block of Dougherty Road.

The officers were conducting the search because a probationer was wanted "in connection with some crimes that had ocurred on a train," Nelson said. "During that search, it appears one officer accidentally fired his weapon, which struck the other officer and ultimately it was a fatal shot."

The injured officer was taken to Eden Hospital in Castro Valley and died there. Neither of the officers have been identified, Nelson said. 

The Dublin Police Department is conducting the investigation into the incident, but is under contract for many services with the Alameda County Sheriff's Department.

"BART has been informed that one of our officers has died from wounds sustained during a shooting earlier today," BART Police Chief Kenton Rainey and and General Manager Grace Crunican said in a joint statement.

"The entire BART organization is deeply saddened by this tragic event," they said, "and we ask the public to keep the officer's family in its thoughts and prayers."

BART's police department came under heavy scrutiny after unarmed passenger Oscar Grant III was fatally shot by an officer at the Fruitvale station in Oakland in 2009. However, a report issued last month by an independent expert found that BART police had made significant progress in enacting reforms.

The expert, Patrick Oliver, noted improvements in the use of force, officer training, community engagement and organizational statements.

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