By David Willis
BBC correspondent in California
A man is to be charged with murdering nine people - all thought to be members of his own family - at his home.
Marcus Wesson is said to be cooperating with investigators
Police arrested Marcus Wesson, 57, on Friday after a standoff in the Californian city of Fresno.
Inside the house police found the bodies of six females and three males aged from one to 25 years old.
Detectives say Mr Wesson has fathered children with at least four women, two of whom are thought to be his own daughters.
It appeared that two women to whom Mr Wesson had once been married had gone there to collect the children, but he refused to allow the women access.
It took investigators hours to establish the exact number of dead due to the fact that the bodies were piled up and entangled in a pile of clothing.
Officers who had gone to Mr Wesson's home after being called over a child custody dispute were so distressed at the macabre discovery that some needed counselling.
Police believe that all the victims are members of Wesson's family, but have not released the names pending notification of kin.
Fresno Police Chief Jerry Dyer said that "there may have been some kind of ritual" involved in the murder, but added that no mutilations had been carried out.
Mr Wesson, who was arrested on Friday after emerging from his home covered in blood, is described by police as "very calm" and is co-operating with the police.
An acquaintance of Wesson's said that the man lived with five women, all of which seemed to have a romantic relationship with him.
The women appeared to be under his control, walked behind him and did not speak unless he was with them.
"The neighbours felt there was some weird kind of polygamy commune thing going on," said Frank Muna - a defence lawyer who sold his burned-out house to Wesson and the women in 1999.
Mr Wesson moved home again eight months ago, partly due to neighbour's complaints.
Fresno, a city some 190 miles (305km) south-east of San Francisco, was shocked over the largest mass killing it had ever witnessed.
"If this does not qualify for the death sentence, then there is no case that would," Chief Dyer said.