The Contra Costa County Sheriff's Office first received a call about the man around 7:15 p.m. on Saturday, when a domestic violence incident was reported on the 4700 block of Appian Way, Sheriff's office spokesman Jimmy Lee said.
The victim in that incident left the scene before deputies arrived, with three children in her car.
Deputies later contacted the suspect, 43-year-old Andrew Harper of El Sobrante, at an apartment on the 4300 block of San Pablo Dam Road, only to discover that Harper was armed with a handgun in a bedroom. The three children were inside the apartment with him.
A perimeter was established and hostage negotiators brought in. Residents in the area were warned to shelter in place away from windows while the standoff continued and traffic was stopped on San Pablo Dam Road. The three children were allowed to leave the apartment unharmed, while talks continued with Harper, Lee said.
At some point during negotiations, several officers perceived a threat from Harper, and at least one weapon was fired toward him. It remains unknown at this point whether he was struck, Lee said.
A SWAT team entered the home around 3:15 a.m., only to find Harper dead. An autopsy to determine the cause of death is scheduled for Tuesday. Anyone with any information on the case is asked to call the Contra Costa County Sheriff's Office at (925) 646-2441.