( CNN ) -- A California transit officer shot and killed another officer Tuesday in an incident that authorities are calling a `` tragic accident . '' The two Bay Area Rapid Transit police officers were conducting a search Tuesday afternoon of a Dublin apartment in connection with a spree of train robberies when the shooting occurred , according to Alameda County Sheriffs spokesman Sgt . J.D . Nelson . During the search , the `` officer accidentally fired his weapon and struck and killed another officer , '' Nelson said . `` This appears to be a terrible and tragic accident . '' The incident is being investigated . BART Police Chief Kenton Rainey said he was `` deeply saddened '' by the incident . The shooting marks the first death of a BART police officer in the agency 's history , CNN affiliate KGO reported . BART train kills 2 workers near San Francisco . Gun safety instructor accidentally shoots student . CNN 's Janet DiGiacomo and Augie Martin contributed to this report .
NEW : This marks the first fatal shooting of officer in transit agency 's history . The shooting happened in connection with a search of an apartment . Authorities are saying the shooting was an accident . BART chief says he is `` deeply saddened ''