Officers arrived at the home after Bonadie's sister called police to say she was worried about her elderly parents, said Sgt. Robert Avels. She told police her brother has a history of mental illness and was refusing to take his medicine and causing a disturbance.
"Family members described his behavior as extreme paranoia (that) people were trying to kill him, poison him," police Capt. Chris Weiske told reporters.
One of the bodies appeared to have been shot at close range, Avels said. Paramedics could not find an obvious gunshot wound on the other body and the cause of death was not immediately clear.
Bonadie was booked on suspicion of two homicides and attempting to kill two police officers who approached the home. No one was hit.
After a SWAT team responded, Bonadie came out of the house and stood there for 20 minutes, brandishing a gun in each hand and glaring at officers. Officers negotiated with Bonadie until he surrendered, Avels said.
Police found assault weapons, other firearms and ammunition strewn around the house, Avels said.
An elementary school across the street was locked down for part of the afternoon.
Montclair is in San Bernardino County, about 35 miles east of Los Angeles.
MORE LOCAL HEADLINES FROM INLAND EMPIRE
SEND TIP || REPORT TYPO || TWEET @abc7 || WIDGET