Police in Tehama County believe Kevin Janson Neal shot her dead on Monday night before he began roaming the streets the following morning, armed with two semi-automatic rifles and selecting targets apparently at random.
"We believe that is what started this whole event," Tehama County Assistant Sheriff Phil Johnston told a news conference.
Detectives initially believed four people had been killed and 10 wounded by Neal, who was out on bail for a suspected assault with a deadly weapon committed in January, before he was gunned down by police.
The mass shooting began around 8:00 am (1600 GMT) Tuesday at a home in Rancho Tehama Reserve and continued at several locations in the community, including an elementary school.
No children were among the dead and the motive for the assault remains unclear, although it may be linked to a domestic dispute and a history of disagreements with neighbors.
Detectives say Neal went on his shooting spree after stealing a neighbor's vehicle and then tried to gain access to the school but was unsuccessful as it was on lockdown.
Neal told reporters the quick thinking of the school's staff had been "monumental" in preventing further deaths.
There were seven children among the wounded, said Johnston, four of whom sustained their injuries at the school and the youngest of whom was two years old.
The elementary school is located on the outskirts of Corning, an olive oil-producing town of around 8,000 people located about 100 miles (160 kilometers) north of the state capital Sacramento.
Neal, who was wearing a military-style vest, left the school to continue his rampage and crashed the vehicle at one point. He then stole a second vehicle and was killed in a shootout.
The shooting coincides with a flare-up of the long-running debate on America's epidemic of gun violence and the ready accessibility of high-powered weapons, less than 10 days after a gunman shot dead 26 people at a church in Texas.
More than 33,000 people die annually in the United States from gun-related deaths -- two-thirds of them suicides, according to the Centers for Disease Control and Prevention.
(Except for the headline, this story has not been edited by NDTV staff and is published from a syndicated feed.)
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