A Patterson High School teacher found three shotgun shells in a classroom a day after a widespread brawl that drew 30 law enforcement officers to the school.
The finding sparked another security scare, but Stanislaus County Sheriff's spokesman Royjindar Singh said the shells were likely dropped at the school on Thursday, after the incident.
Deputies swept through all the classrooms on Wednesday, the day of
the melee, and didn't find them, he said.
The shells were "meant to be found," and left in the school as a prank or an act of intimidation, Singh said.
All nine students who were arrested are facing expulsion, Superintendent Patrick Sweeney said.
"We believe it was planned fights between rival gangs," Sweeney said.
Other schools in Stanislaus County increased security as a precaution, officials said.