It happened in the area of Shannon and Windflower Way.
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UPDATE: 18-year-old arrested in Oakley party shooting that left teen dead, police say
Three other victims were taken to the hospital. Police say their conditions are non-life threatening, according to Oakley Police Chief Paul Beard in a Facebook post. They were taken to John Muir in Walnut Creek.
Chief Beard said police were dispatched to the home around 11:12 p.m., 30 minutes before the shooting following a noise complaint.
Police say they spoke to an 18-year-old woman who lives in the home and began to shut down the party, declining assistance from officers.
A witness told police more than a dozen people showed up to the home after officers left, but the front door was locked. Police then said the group entered the backyard through a side gate.
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Minutes later, police said there was screaming from the home and several people were seen running out the front door.
Approximately five to six gun shots were heard, police said.
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They said they found 9mm shell casings in front of the home.
Video from the scene shows people walking around in costumes, though it's unclear if it was a Halloween house party.
Police said the suspect fled prior to officers arriving on scene. They believe there is only one suspect at this time.
Neighbors were shocked for this to happen on what they describe as "a very quiet street."
One neighbor and her family were witness to the chaos.
"Two of them ended up on the front lawn, a girl and a boy both shot...You could hear just another young man just like screaming and wailing."
The scene was so frantic, you could still see a bowl of chips someone dropped on the lawn while running away.
"Everyone is shocked and devastated that this happened at all, let alone here," another neighbor Tracy Nelson said. "It is not something we really see or hear here in Oakley."
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Neighbor Dustin Lewis was alarmed.
"Basically, hearing a bunch of noise, loud screaming like a fight was going on outside so I came out and at that point, there were already people running down the street - scared," Lewis said. "Was shortly after that I heard six shots went off."
He called 911 as chaos ensued.
"It was at least 100 or 150 kids that were running out here. There could have been 200 there were so many," he said. "Their innocence was lost. You can see the terror in their faces, in their eyes, running, and having to experience that."
Students scared after fatal shooting at high school party
Most of the students in the neighborhood go to Freedom High School where there was a heavy police presence Monday. Parents clustered outside the school doors as rumors circulated. Some students left class.
A 17-year-old high school senior said, "They said that there was a rumor that the person from the party was going to come and shoot up the school, and we felt very unsafe being here and just wanted to get away.
You walked off campus because your parents were worried? ABC7's Leslie Brinkley asked.
"Yes, and I was worried for my own safety being here."
Witnesses told ABC7 News that students from three high schools -- Freedom, Liberty, and Heritage -- were present at the party. At Liberty High School, counselors were available to students who were traumatized.
The victim has not been publicly identified, but next of kin was notified. Police believe there is only one suspect.
People living on the street are left wondering how they can return to that quiet peaceful space.
"Hopefully no one ever experiences something like this again," one neighbor said.
If anyone has information, they are asked to call the Oakley Police Department at 925-625-8060.
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