Nearly 40 years after a vicious murder spree that claimed seven lives, investigators on Tuesday are set to begin digging at Charles Manson's former Death Valley ranch in search for new victims of the hippie killer.

Police officials, along with criminology specialists, will be looking for disturbed soils and chemical markers that may indicate unmarked graves they suspect could hold up to four more victims.

• Click here to see photos of Charles Manson and the ranch.

Few criminals have captured the nation’s attention like Manson, who appeared in court in 1971 with an X carved in his forehead, declared himself the devil and attacked the trial judge.

Manson, who is serving a life sentence at Corcoran State Prison in California, was responsible for the murders of the pregnant actress Sharon Tate and six others.

Some investigators have long suspected there could be more, and say the cult was responsible for the disappearances of several women and drifters.

“One of the girls up on the ranch didn’t get along with the others. She took a walk with Manson . . . and no one ever saw her again,” said Emmett Harder, a former Manson neighbor and local prospector.

Last month, Harder led a team of investigators and forensic experts to Barker Ranch, a remote, turn-of-the-century ranch house Manson and a dozen followers took over in the summer of 1969 following their two-day murder spree.

The investigative team brought a battery of high-tech detection tools to help locate the skeletons of up to four victims police believe the Manson clan may have murdered 39 years ago.

“Those bones will continue to retain some organic material, and that material can last 30-40 years,” according to Dr. Elizabeth Miller, a forensic anthropologist and consultant to the TV show “Bones.”

Investigators began their new search after a four-year-old cadaver dog named Buster visited the Barker Ranch and "altered" to several spots, suggesting human remains were buried there. His handler, Paul Dotsie, is a local cop with a lifelong curiosity about the Manson family.

Following Buster’s discovery, other cadaver dogs corroborated the possibility of human remains on site.

Detectives with the Inyo County Sheriff’s Office also brought in a chemical sniffer, a laser that detects bone and teeth fragments and ground-penetrating radar to survey Barker Ranch. While the results were not conclusive, Sheriff William Lutze said he hoped the search team would finally confirm or put to rest speculation more Manson victims are buried at the ranch.

The expedition to the secluded ranch is expected to last through Thursday and will take investigators into the Panamint Mountain range, within Death Valley National Park. The National Park Service has closed the ranch to the public for the duration of the dig.

The Associated Press contributed to this report.