The party was held Monday night in a residential neighborhood in Bloomington. Neighbors describe it as a disruptive event, with cars everywhere, plenty of noise and partygoers spilling out into neighborhood streets. The sheriff's department estimated some 300 people were there.
One neighbor said she and other residents of Geronimo Avenue called the sheriff's department, but the event continued.
The shots rang out around 1 a.m.
"The young people run everywhere!" the neighbor said. "We stay inside the house."
When deputies arrived, they found a teenage boy with gunshot wounds. He was taken to the hospital where he was pronounced dead.
The principal at Alta Loma High School in Rancho Cucamonga identified the victim as one of their students, sophomore Robert "Robbie" Plyley.
He said guidance counselors and therapists were being made available for students.
"Robert was a wonderful young man and his loss will be felt deeply by our entire school and District community," said Mathew Holton, superintendent of the Chaffey Joint Union High School District. "We are taking the necessary steps to support our students and staff, and will gather a team of counselors and therapists who will be available to provide additional support."
Investigators with the San Bernardino County Sheriff's Department remained at the scene Tuesday, where debris from the party - and possible evidence - could be seen along a 300-foot stretch of Geronimo Avenue, from shoes to cups and bottles, parts of Halloween costumes and even phone chargers.
No description of a possible suspect or the circumstances that led to the shooting have been made publicly available.
"It's very sad, he was very young," said student Jacqui Mendoca. "I heard today. We're just devastated at Alta Loma High School. And we're having conferences and just sad. He was a very young boy."
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