A California man killed his wife and hid her body in his home before he went on a gun rampage and fatally shot four people, police have said.
“We believe that’s probably what started this whole event,” Tehama County Assistant Sheriff Phil Johnston told reporters on Wednesday.
Kevin Janson Neal, 43, fired into an elementary school in Rancho Tehama, but was stopped from entering by teachers.
His wife’s body was found hidden under floorboards, police say.
“This individual was literally going up and down the road and shooting at random structures,” the assistant sheriff said.
“So it is possible that you may have a neighbour or somebody that could be injured or hurt that we are not aware of,” he added, urging residents to check on their neighbours.
A motive for the attack is still unclear, but Mr Johnston said: “I think he had a desire to kill as many people as he could.”
Authorities praised teachers’ for locking down the school campus after hearing gunshots, saying their actions were “monumental” in saving “countless” lives.
Fourteen people were injured in the rampage, including seven children, police say.
One child at the school was shot in the chest, but other children were mainly hurt by broken glass, the sheriff said.
The family of Alejandro Hernandez, 6, created a GoFundMe account to help raise money for his healthcare costs after he was shot in the chest and foot at school.
Police say that two semi-automatic rifles – also known as assault rifles – that were used by the gunman were recovered from one of the crime scenes.
Mr Johnston said the guns were obtained “in an illegal manner” and manufactured illegally.
During the attack, Neal also wore a a military-style assault vest capable of storing multiple rounds of ammunition.
Police said Neal was out on bail after he posted a $160,000 (£121,000) bond for an assault with a deadly weapon charge, which stemmed from an incident with his neighbours.
A woman, who identified herself as Neal’s mother, told the Associated Press news agency that Neal called her before the attack and said: “I’m on a cliff and there’s nowhere to go.”
She said Neal was in a long-running dispute with neighbours who he believed were cooking methamphetamine.
She added that Neal, who was raised in North Carolina, had been working as a cannabis farmer and had recently married his long-time girlfriend.
His sister, Sheridan Orr, told the AP that she believed her brother was addicted to drugs and struggled with mental illness and a violent temper.
“We’re stunned and we’re appalled that this is a person who has no business with firearms, whatsoever,” Ms Orr said.
She added that she hopes this attack will “make people realise there must be some gates on people like this from getting guns”.
“This is the same story we’re hearing more and more.”