Police this week arrested five people in connection with a fatal Halloween house party shooting in northern California, including the party’s promoter, and the sheriff said Friday that there were several armed people and members of rival gangs there.

A specific motive in the shooting in Orinda that left five people dead has not been determined, Contra Costa County Sheriff David Livingston said at a news conference Friday.

"We're still identifying specific motive, but I can tell you there were rival gangs involved in the altercation inside the home,” he said. “We are told by certain witnesses there was also an attempt to steal property from one person to another, which may have precipitated the initial round of shootings.”

"We believe that some involved in this event went to the party with the intention of causing harm and conflict," Livingston said.

The shooting occurred at around 10:50 p.m. on Oct. 31 at a home that was rented through Airbnb, officials have said. Airbnb said it was banning "party houses" in the wake of the shooting.

The arrests of the five people occurred Thursday in several cities in the San Francisco Bay Area and in Antioch, which is northeast of Berkeley and northeast of Orinda, a community of around 20,000, the sheriff’s office said.

Lebraun Tyree Wallace, 28, of San Mateo; Jaquez Deshawn Sweeney, 20, of Marin City; Jason D. Iles, 20, of Marin City; and Shamron Joshua Mitchell, 30; were arrested and booked on murder and conspiracy charges, the sheriff’s office said.

Devin Isiah Williamson, 21, of Vallejo, who Livingston said was the promoter of the event, was arrested and booked on charges of conspiracy, carrying a concealed weapon, and vandalism, Livingston said. It will be up to the district attorney’s office to file formal charges.

Sweeney "was the subject that was seen entering the residence in Orinda with a firearm," and when he was arrested he was found to have been carrying a 9 mm pistol, Livingston said.

Jason Iles, Lebraun Wallace, Devin Williamson, Jaquez Deshawne Sweeney, and Shamron Mitchell. Contra Costa County Sheriff's Office via AP

Two of those found dead inside the residence were also armed, and they have criminal records and are believed to have been associated with gangs in San Francisco and Marin City, Livingston said.

Authorities did not say how many shooters are believed to have been involved, but Livingston said Friday that “we can safely say there were multiple shooters at this event."

"At the front of the home where there was so-called security — in actuality, people were clearly seen secreting firearms in their pants," the sheriff said. "So, there were many firearms inside that party that evening and we’re trying to track down and get a specific number on it."

He said that he personally went to the scene and it was "a bloodbath" with many shell casings on the floor and on counter tops.

"In my 32 years of law enforcement I have never seen a homicide scene like this, ever," Livingston said.

Police were on the way to investigate calls of a loud party minutes before the shooting was reported, the sheriff's office has said.

Livingston said those calls are typically low priority and the office gets to those when able, and that the sheriff’s office had been assisting the city of Livingston that night on another violent call.

He said the blame of the shooting doesn’t lie with Airbnb, the home owners, or the police.

"The blame rests specifically on the individuals that carried guns into that party, pulled the trigger and murdered someone," Livingston said.

In addition to the five people killed there were five other victims, three of whom were shot. Others suffered serious injuries while fleeing, he said, including one person who jumped from a 30-foot balcony.

Investigators have video from neighbors as well as from cell phones and other sources, Livingston said.

He said that from the scene and search warrants, four firearms have been recovered so far.

Livingston stressed that the investigation is ongoing, and he said “I do believe that we will have additional people in custody at some point soon."