The Barker Ranch was the last redoubt of the gaggle of hippies, hitchhikers and lost souls that called itself the Family and followed the twisted beliefs of the convicted pimp, sex offender and would-be musician Charles Manson.

It was to this lonely outpost in the California desert that the group of 26 came after committing the gruesome Sharon Tate and LaBianca murders, and it was here, on August 12 1969, that Manson was arrested hiding under a bathroom sink.

The story of how Manson came to form his sex and drug-fuelled cult, and turned his followers' adulation into blood lust, has become the stuff of criminological legend, marking the low point of the 60s revolution. Members of the Family were prosecuted for nine murders, the most famous victim being Tate, the pregnant wife of the film director Roman Polanski, but rumours have consistently claimed that the true death toll was much higher.

Now a group of interested individuals - including Tate's younger sister, Debra, a local police detective, and forensics experts - have begun searching the desert around the ranch and believe they have found evidence of two, perhaps three, human graves that may be linked to the Manson Family.

The local sheriff's office in Inyo County, about 200 miles from Los Angeles, is expected to decide next week whether to order an official dig of the potential grave sites to follow up on the amateur sleuthing. The sheriff is weighing up the cost and police time that would be involved against the public interest in bringing closure to one of America's most notorious criminal sprees.

The team of investigators made use of technology that was unavailable in 1969 to identify what they believe are sites where human remains are buried. Sergeant Paul Dostie, a local police officer working off-duty, used his sniffer dog that has been trained to detect the smell of bodies, and researchers from a laboratory in Tennessee used ground probing equipment and radar to detect signs of refilled holes in the ground.

Debra Tate, who has dedicated her life since her sister's murder to preventing any of the jailed Family members being released, is insistent that the excavation should take place. She told an LA television station: "If there's a chance that we can send some children home, then we need to do that."

There has long been conjecture that Manson may have been responsible for more murders than those ascribed to him and the four members of the Family who he got to do his bloody bidding. An informant who associated with Manson in jail has said the cult leader once confessed that he had killed 35, though such bragging from a recognised psychopath and fantasist must be treated with a degree of scepticism.

Susan Atkins, one of the Manson devotees who was involved in the murders and like him is serving a life sentence, was also said to have bragged to her cell mate soon after she was arrested that there were "three people out in the desert that they done in".

Tales have swirled around Death Valley, where the Barker ranch is located, that Manson and his main accomplice, Tex Watson, took a woman who was proving to be awkward within the group for a walk away from the building into the desert, returning an hour later without her. Dostie said the first site that received the attention of his sniffer dog fits the description of the direction in which they had been walking.

An abandoned haversack was found at the ranch, leading to speculation that its owner may also be a victim.

In nearby Bishop police have reopened the case of Fillippo Tennerelli, who was thought to have killed himself in a motel room in 1969 but is said to have been a victim of the Family.

Police are taking seriously the findings of the amateur investigators, though they have pointed out that loose ground resembling a burial site can be created by animals, and that even if there are human remains present they could be those of a prospector or rancher from long ago.

"At this point we're looking at whatever shreds of evidence we can gather," police chief Kathleen Sheehan told the Associated Press. "There's no statute of limitations on murder."

The murders

"Maybe I should have killed 400 or 500 people, then I might have felt better." So said Charles Manson, speaking from high-security prison.

In the 39 years since he orchestrated the multiple murders known as the "two nights of madness", fascination and revulsion at his acts have only grown more intense.

He used his power over his cult members, many of whom were women, initially to bond them into a virtual state of sexual and domestic servitude, and then to persuade them to commit brutal slayings at his command.

Manson told them that the murders were all part of an apocalyptic vision of the future which he called Helter Skelter, named after the song on the Beatle's White Album which had recently been released. America, he said, would erupt in a racial war between whites and blacks.

Manson sent four of his followers out on the night of August 8 1969 and told them to break into the mansion owned by Roman Polanski and Sharon Tate. Polanski was filming in London, but Tate - who was more than eight months pregnant - and four other people were murdered, and the word "pig" scrawled in blood on the front door.

The next night Manson himself and six Family members murdered Leno and Rosemary LaBianca, writing "Helter Skelter" in blood on their fridge.

Manson was sentenced to death, which was later commuted to life imprisonment.