3 LA County sheriff’s deputies killed by explosion at training facility, the agency’s largest loss of life since 1857

(CNN) — An explosion at a Los Angeles County Sheriff’s Department training facility killed three veteran members assigned to the agency’s arson and explosives detail Friday morning – a tragedy that marks the “largest loss of life” at the department since 1857, according to Sheriff Robert Luna.

The explosion is believed to have been an accident. Federal and local investigators began working to determine what led to the explosion after the scene was rendered safe by the Los Angeles Police Department’s bomb squad just after 11 a.m. local time, Luna said at a news conference.

It’s unclear whether the incident was related to a training session or whether officers were handling evidence, a senior law enforcement source familiar with the incident told CNN.

The three sworn members had collect