A San Francisco Bay Area Rapid Transit officer was accidentally killed on Tuesday, after another law enforcement official shot and killed him while they were searching a suspected thief's apartment.

Investigators are still unclear on the details concerning 42-year-old BART Sgt. Tom Smith's death. Sheriff's officials visited the site of the killing in Dublin for answers, the Associated Press reported.

"That's going to be part of the investigation, to find out if this was some sort of an accidental discharge or whether it was a case of target misidentification," Sgt. J.D. Nelson of the Alameda County Sheriff's office told KTVU on Tuesday. "Either way, it was an accident, and we're going to try to figure out exactly what happened and the circumstances that led up to it."

Smith lived with this wife and 6-year-old daughter in San Ramon, according to a statement released by Gov. Jerry Brown.

"Sergeant Smith's family, friends and colleagues are in our thoughts as we honor his service during this painful time," Brown wrote on Tuesday.

Smith and the officer who shot him were reportedly part of BART's detective unit, according to the Associated Press. The two were searching the apartment of a man who is under investigation for allegedly carrying out robberies on BART property, AP reported. The man was in custody, and wasn't home at the time.