Several people were shot dead while watching a football game at a central California home on Sunday, police said.
Police were called to the scene after at least two people snuck into the backyard of a home in Fresno, around 320km north of Los Angeles, and opened fire.
"What we found were several individuals deceased in the backyard," said Fresno police spokesperson Bill Dooley.
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Local media outlets reported that four people were killed. Police have not released a death toll but said nine people had been shot in the attack.
Dooley said police were looking for surveillance footage and witnesses to track the suspects.
