Detectives have not determined a motive or identified a suspect.
Coroner's investigators were sent to the scene to identify the victims and determine how long they had been dead, Luna said.
Some of the victims had been shot more than once, said Ed Winter, assistant chief in the Los Angeles County coroner's office.
Dozens of detectives combed the area for evidence.
"Because of the rains last night and the heavy foliage in the area where the crime occurred, the investigative process will be slow and methodical," Luna said.
Police initially described the victims as homeless but now say they haven't confirmed that. Officials also were also trying to track down the person who tipped police.
"That's a piece of the puzzle that we're trying to figure out," Luna said. "We're hoping that person comes forward and tells us, 'This is what I saw or heard."'
"The way they were situated, it was perfect in that no one can find the crime scene or see it," he added.
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