The gunman, who killed four people in a string of shootings in northern California on 14 November, began his deadly rampage by killing his wife and stashing her body beneath the floorboards of their home, the police has said.
CNN quoted a police official as saying that Kevin Neal, who was identified as the gunman, shot and killed his wife the previous night and hid her body under a floor in his residence.
"We believe that's probably what started this whole event," Tehama County Assistant Sheriff Phil Johnston said
According to CNN, the discovery of the spouse's body brought the death toll to six, including the gunman.
Neal, 44, had been out on bail after being charged with stabbing a neighbour.
The police said that Neal was no stranger to law enforcement and that prior to the rampage on Tuesday, his neighbours had reported shots coming from the residence.
The shooting incident took place near the Rancho Tehama Elementary school when some parents were dropping off their children.