Police discovered nine bodies intertwined in a pile of clothes at a Fresno home and 10 coffins stacked along a wall, and were trying to determine if some ritual was involved in the slaughter.
A 57-year-old man surrendered to police after walking out of the house covered in what appeared to be blood.
The victims were seven children ranging in age from 1 to 8, a 20-year-old woman and a 17-year-old girl. All were thought to be the children of Marcus Wesson (search), whom police handcuffed following a brief standoff.
Authorities said Saturday that Wesson had been arrested on suspicion of killing the victims, but wouldn't comment until an afternoon news conference on what charges prosecutors might file.
The grim scene caused even veteran officers to weep.
Police Chief Jerry Dyer (search) wiped tears from his eyes as officers carried the bodies from the home, cradling the youngest ones in their arms.
"I've been with the Fresno Police Department (search) for 25 years, and I've never experienced anything of this nature," he said.
Dyer said the victims probably were Wesson's children.
"There may have been some type of ritual involved," he said.
Officers were originally called to the scene Friday afternoon for a child custody dispute.
Ten coffins lined a wall inside the home's front room. The bodies were so entangled in a pile of clothing that it took hours for investigators to reach a final count, police said.
The police chief declined to say how the victims died, but the scene was so gruesome some of the first officers into the house were placed on administrative leave and were being counseled Friday night.
Six police chaplains were at the house throughout the evening as detectives continued to gather evidence.
Officers were called to the home Friday afternoon by two women who said a man had their children and would not release them.
The man initially ignored orders to come out, running into a back bedroom as two other women fled the house. They were unharmed.
Police believe the suspect fathered the victims with the four women. They did not identify the women or the victims.
A neighbor, Chris Tognazzini, said he heard two gunshots moments before police arrived.
Dyer said the women who called authorities told them they had given custody of their children to Wesson two years ago and now wanted them back.
The slayings shocked authorities in Fresno, a city of 440,000 about 190 miles southeast of San Francisco. Dyer said the city had seen three murders in the last 2½ months, the fewest number for a 10-week period in more than three decades.
"The only thing we can do now is mourn. We mourn for the kids, we mourn for the police," said Mayor Alan Autry. "We will never be the same again."
Neighbors who milled around outside said they knew little about Wesson or the house where a large yellow bus was parked in the driveway.
"He never said 'Hi,'" said Linda Morales. "I'd drive by and he'd make a point to turn his face."
Another neighbor, Johnny Rios, said that on many nights he heard loud banging coming from the house, as though the people inside were building something.
"There was something up over there," Rios said.