Scientists and crime scene investigators today began excavations at the ranch that was once home to the convicted murderer Charles Manson.

Manson is serving life at Corcoran state prison after he and six others murdered the pregnant actress Sharon Tate, three of her friends and a teenager at her Los Angeles home almost 40 years ago, and killed another couple the following night.

He and his followers fled to Barker Ranch after the massacre. A member of Manson's family later suggested more bodies had been buried there.

It was decided to evacuate the site after scientists, police and National Park rangers found evidence to suggest that at least two areas could be graves.

"The evidence is indicative enough to why we're out here today," said Arpad Vass, an expert in identifying and analysing the chemicals given off by human bodies as they break down over time.

After further soil sampling, which yielded inconsistent results, Sheriff Bill Lutze agreed to the exploratory excavation. The ranch site has now been closed to the public.

Today's excavation - the first of two digs planned over three days - will be limited to removing thin layers of dirt from a small area.

The painstaking work is designed not to disturb any evidence of bodies that would now be decades old.

The rugged terrain is accessible only by four-wheel drive vehicles, and researchers said the nature of the soil — dry and rocky — made it difficult to operate some of the new forensic tools being used.

"We've got a lot riding on this," Paul Dostie, a Mammoth Lakes police sergeant, said.

"We have the science and law enforcement coming together, and this is a first. We're really looking to see how all these technologies come together."

For years, rumours have circulated about other possible Manson victims, including hitchhikers who visited the ranch and were not seen again, and runaways who drifted into the camp before falling out of favour.