She has been identified as 19-year-old Oshiana Tompkins of Vallejo/Hercules.
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Police also identified Friday four men killed as 22-year-old Tiyon Farley of Antioch, 24-year-old Omar Taylor of Pittsburg, 23-year-old Ramon Hill Jr. of San Francisco/Oakland and 29-year-old Javin County of Sausalito/Richmond.
A quiet Halloween night erupted in gunfire just before 11 p.m. in an Orinda neighborhood high in the hills on Lucille Way, where a shooting at a house party left four people dead, and at least four others injured.
"When the officers arrived, the encountered at least 100 people running from the home," said Orinda Police Chief David Cook.
A video posted on social media that shows the house crowded with people earlier in the evening.
"He got shot like about 3 or 4 times," said Romond Reynolds, who told reporters his 24-year-old son Armani Reynolds was among those shot. Romond Reynolds said his son is in stable condition at a local hospital.
A flyer circulated on social media called the event a Halloween Mansion Party. Invitees were instructed to direct message the host to get the address.
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Neighbors say the home where the shooting occurred is often rented out on the website Airbnb and there have been large parties there before.
"It was terrifying in the first moments. The neighbors didn't know what was going on," said neighbor Chris Gade, "but now it's just kind of frustrating."
Orinda City Manager Steve Saloman revealed several complaints about large parties at the home in the past nine months--most recently an email at 9:35pm Thursday night, just 1 hour and 15 minutes before violence erupted.
"I believe they tried to call police, or they did call the police as well," said Salomon.
Later, Contra Costa Sheriffs told ABC7 News, that there were at least two noise complaints called in: "Orinda Police Officers were yesterday (Thursday) called to the house at 9:19pm and 10:25pm regarding a noise complaint. At 10:48pm, an officer was headed to the home to investigate the calls. The initial reports of shooting came in around 10:50pm."
The owner of the home told the San Francisco Chronicle that she rented the house to someone who claimed it would be used for a small family reunion. Orinda's ordinance on short-term rentals limits occupancy to 13 people.
Orinda Mayor Inga Miller said the City Council will be reviewing that ordinance at its next meeting on Tuesday, but that the first priority is those hurt and killed at the house party.
"Our hearts go out to the families who are learning about their loved ones," said Miller.
Orinda's last homicide was in 2012.