RICHMOND >> At least one Richmond police officer shot and killed someone during a warrant service Tuesday night, but as of Wednesday afternoon police had not said why.

While the local cops remained mum on the shooting, the California attorney general’s office announced it is launching its own investigation. The AG’s office cited a state law allowing it to probe incidents where police fatally shoot someone who wasn’t armed with a deadly weapon at the time.

The police shooting occurred a little before 9 p.m. Tuesday near the 300 block of Carlson Boulevard in south Richmond. Police had earlier responded to an area across the railroad tracks on the 2700 block of Maine Avenue.

A Richmond police news release says officers showed up around 8:15 p.m. and were attempting to arrest a person on suspicion of violating his probation by committing an act of domestic violence.

The person refused to surrender. The person was shot roughly 30 minutes into the standoff.

Police haven’t said what prompted the shooting, nor have they identified the dead person by name, age or gender. The news release says officers spent the half hour attempting to de-escalate the situation before killing the person.

Contra Costa County launched its own protocol, invoked anytime a person is killed by police or dies in police custody countywide. As part of the county’s investigation, the sheriff will hold a coroner’s inquest where a local jury will look into the matter.

Police haven’t said how many officers fired, or named any of the officers who did. The news release says the department is “committed” to a “thorough and transparent” investigation.

It’s the first police killing this year in Contra Costa.