Parts of a human skull were found on Thursday on a property connected to convicted killer Wesley Shermantine during a search by deputies from two California counties, acting on a tip from the killer, Fox40 News in Sacramento reported.

The gender and other characteristics of the skull, found by cadaver dogs from Santa Clara County, have not been identified, and no other bones were found near it, according to the station.

Because it was found alone, investigators do not know how it ended up just beyond the Shermantine property line in San Joaquin County -- whether by an animal, person or even nature.

Shermantine began a killing spree in 1984 with his crime partner, Loren Herzog, and the two became known as the “Speed Freak Killers.” Authorities think they killed as many as 19 people.

They were both convicted of the murders of Cyndi Vanderheiden and Chevelle Wheeler, along with others. The women’s remains were never found.

Shermantine, now on death row, recently wrote a letter to a newspaper claiming to point authorities where the bodies of his victims were, sparking the new search. Authorities have contacted the Vanderheiden family to inform them of Thursday’s discovery.

“These guys killed my daughter,” John Vanderneiden told the station. “This is like reliving it again. We still haven’t found her.”

This is not the first time Shermantine has offered to help police locate the bodies. While on trial in 2001, he offered police information in exchange for $20,000. Officials refused the offer. After word got out of his latest attempt to point authorities to the bodies, Herzog, who had since been release from prison, hanged himself at home.

Investigators, after searching all day Thursday with shovels and cadaver dogs, told Fox40 that they had yet to find more remains at the property.

Click here for more information on this story from Fox40 Sacramento.