SAN FRANCISCO - The FBI is preparing to search one of four abandoned wells in California recently singled out by convicted “Speed Freak” serial killer Wesley Shermantine as a site where he and his partner in crime disposed of their victims’ bodies.

The San Joaquin County Board of Supervisors agreed on Tuesday to spend up to $200,000 for an FBI-supervised contractor to conduct excavations in and around the well and unearth its contents, expanding a months-long quest for human remains linked to the killers.

“Everyone’s goal, if there’s remains in these wells, is to recover them and return them to their loved ones,” said Les Garcia, a spokesman for county Sheriff Steve Moore.

Shermantine and his now-deceased co-defendant, Loren Herzog, have long been suspected in as many as 22 deaths, mostly of young women and girls who vanished during the 1980s and 1990s.

Ultimately convicted in connection with six slayings, they were dubbed the Speed Freak killers for the methamphetamine-fueled violence they unleashed in and around California’s farm-rich San Joaquin Valley.

In recent months, Shermantine has suggested in letters to reporters and others that the pair may have been responsible for more than 70 killings, a claim which if true would rank the duo among the most prolific serial killers in U.S. history.

Crude maps drawn by Shermantine after more than a decade of silence on the fate and whereabouts of his victims helped lead authorities in February to the skeletal remains of five teen girls and young women.

Two were unearthed from shallow graves in San Andreas, 100 miles (161 km) northeast of San Francisco, and three were found in a nearby abandoned well adjacent to a former cattle ranch in the San Joaquin County town of Linden.

A bag of remains returned by sheriff’s deputies to the mother of one victim was later determined by a forensic anthropologist to contain commingled fragments of at least two other people, one believed to be a long-missing child.

Then in a rare step state lawmakers authorized earlier this year, Shermantine was briefly released under guard from his death row cell in August to personally guide FBI agents to further sites he claimed were dumping grounds for his victims.

His unusual daylong furlough led authorities to four more defunct wells. Garcia said the FBI would direct drilling and excavation work at one of those sites in the near future.

FBI spokeswoman Gina Swankie declined to say when the work would begin.

A jury convicted Shermantine in 2001 of four murders, and Herzog was found guilty in a separate trial of three slayings, one that overlapped with Shermantine’s case.

While Shermantine was later sentenced to death, Herzog’s conviction was reduced on appeal to a single count of manslaughter, and he was paroled after 11 years in prison.

But Herzog committed suicide by hanging in January, just hours after learning that Shermantine was starting to pinpoint grave sites. (Editing by Steve Gorman and Lisa Shumaker) REUTERS