At around 7 p.m. local time on Monday, LA news helicopters caught images of more than 100 people gathering at the rented mega mansion -- some inside, poolside and others on various balconies overlooking the back yard.
Neighbors complained about noise and parked cars obstructing the roadway outside the rental home, according to Los Angeles Police Department officials. That prompted police to make their first visit to the home Monday evening.
"For us that was the primary concern at the time, to make sure nobody gets killed on the streets," Los Angeles Police Department Lt. Chris Ramirez told CNN.
He said police left the scene after several vehicles were cited and moved, and noise complaints were resolved.
By 1:15 a.m., police officials said they returned after a report of shots fired. They found two women and one man on the driveway. One of those victims, the 35-year-old woman, died at the hospital.
In the chaos that followed the shooting, many partygoers fled the home. Police said another woman took herself to the hospital and is stable, while another man was transported from the surrounding area and checked in and out of the hospital, according to Ramirez.
The victims have not yet been identified, and a motive for the shooting is still unclear, Ramirez said. No arrests have been made.
However, police officials are investigating a gambling match in the home, as well as various social media posts about the party.
"We are treating this as a gang-related homicide," he added.
California Gov. Gavin Newsom rolled back the state's reopening plans on July 13, amid surges in coronavirus.
The gathering drew a rebuke from state health officials.
"It sounds like a high risk experience for those who were there and frankly for the loved ones that they go home to," Dr. Mark Ghaly, California's Health and Human Services secretary, said at a press conference on Tuesday.
A spokesperson for Los Angeles County Public Health Department did not immediately respond to CNN's request for comment.
Police said they were aware of the news footage showing what appeared to be a violation of Los Angeles County's ban on large gatherings, but said that there wasn't much they could do.
"It's really hard to enforce something like that, especially when it's a private party," Ramirez said. "If it's a public gathering it might be different ... It's like me going into your house and telling you what to do in your own property."
According to KCAL-TV, the company that manages the short-term rental property said it was the first it had heard of the party. The company told the CNN affiliate that it had advised the renters that the party was a serious violation of the rental agreement.