The victims - five people shot to death over the weekend at a spot inhabited by the homeless - were known largely by their nicknames or just their first names.
And Southern California's first significant rain of the season may have washed away evidence.
Police in Long Beach are confronted with a baffling murder mystery.
"There is still a demon out there killing innocent people," said Don Morgan, 58, who was friends with the victims. "Satan was here that day."
Three men and two women were found slain Sunday in the seedy neighborhood of warehouses and apartment buildings near the intersection of two freeways. Some of the victims had been shot more than once.
Officers responded to an anonymous call about 8:30 a.m., reports CBS Station KCBS in Los Angeles. They found the bodies near the Santa Fe Avenue off ramp of the San Diego 405 Freeway, close to West Wardlow Road and the 405 interchange with the Long Beach 710 Freeway, Long Beach police Sgt. Dina Zapalski, told KCBS.
But even the time of the attack is in dispute: Some neighbors reported hearing gunfire, yelling and a car speeding off just after midnight, while the coroner said the crime occurred sometime Saturday afternoon or evening.
Police said Monday that they had no eyewitnesses and no suspects and had yet to establish a motive for the slayings. But neighbors said people would often drop by to do drugs in the shadows underneath the freeway.
Investigators spent 12 hours collecting evidence, removing dozens of bags of trash and belongings from the spot in hopes of finding clues. And they issued a plea for the anonymous caller to come forward in the hope that he had more information.
Gang graffiti was sprayed along a freeway bridge near the crime scene, and a drainage channel appeared to be the only way in and out of the spot.
"We have a tremendous amount of foliage out there," Police Chief Anthony W. Batts said. "It's very tough getting into."
Authorities identified two of the victims as Vanessa Malaepule, 34, and Lorenzo Perez Villicana, 44. The others' names were withheld until their families could be notified. Police said they had not determined how many of the victims were homeless.
Morgan said he knew the victims only by their first names or nicknames - LV, Vanessa, Cat, Sammy and Fred. They liked to come to the site to party, he said.
Relatives of Malaepule said she was the mother of six children and was not homeless but liked to hang out at the spot. They said they did not know why.
Her uncle Ilager McMoore said police told him that his niece was found beneath the body of her boyfriend, as though he had tried to shield her from the gunfire. McMoore said he suspects the boyfriend may have been involved in a gang dispute.
Tippi Briggs, a nearby resident, said she had seen an increase in what she suspected was drug activity in the area. "You see people drive up in their nice cars, go in there, then come out after a couple of minutes," she said. "Some are stumbling."
She also said the area had been plagued in recent weeks by a rash of home and car break-ins.
Elsa Neal, who manages an apartment complex close to the scene, said the area was frequented by homeless people and by those who apparently hung out to do drugs. She said the homeless people would sometimes stop by to ask to use her water to clean their cooking utensils and were always polite.
About 10 relatives of Malaepule assembled a shrine on a tattered piece of old carpet, placing a smiling photograph of her atop a bunch of yellow and white flowers. One of her children sprinkled petals around lit candles.
The impromptu memorial was interrupted by a California Highway Patrol officer who told the family they were too close to the freeway and needed to move along.