Three Los Angeles County Sheriff’s Department deputies were killed Friday in an explosion at a training facility in East Los Angeles, a tragedy Sheriff Robert Luna called his agency’s deadliest day since 1857.

Officers spent hours searching a Santa Monica apartment building where the device that exploded and killed three deputies may have originally come from.

Local, federal and state officials are beginning their investigations into the explosion at an East Los Angeles sheriff’s training facility that killed three deputies Friday morning, Sheriff Robert Luna said.

At least three people are believed to have been killed in a huge explosion at a Los Angeles sheriff's department training facility, according to emergency services

The DOJ says it wants info on undocumented immigrants with criminal records. LA County Sheriff Robert Luna says his department doesn't have info on inmates' citizenship status.

The SEB is made up of dozens of highly trained, highly specialized deputies who do everything from SWAT standoffs to risky rescues of people in peril in remote areas.