The tedious and grisly search for the long-lost victims of two California serial killers continued Friday with the addition of dogs specially trained to sniff out human remains.

San Joaquin County sheriff's deputies and other searchers this week have extracted some 1,000 human bone fragments from an old well near the farming town of Linden, about 80 miles east of San Francisco. They hit bottom Thursday and spent Friday examining piles of debris taken from the well while ensuring the well itself was thoroughly searched.

The bones are being sent to the California Department of Justice for possible identification through DNA analysis.

Department spokesman Les Garcia said Friday that authorities are using specially trained "cadaver dogs" to examine the debris piles and determine whether other nearby wells also contain human remains. There's a possibility that another well will be dug up, depending on what the dogs find.

The dogs are on loan from Santa Clara County and are the same hounds that turned up two sets of human remains in Calaveras County two weeks ago that were tentatively identified as two women Wesley Shermantine was convicted of killing and burying on property once owned by his family.

Searchers are pursuing information provided by Shermantine, one of the two so-called "Speed Freak Killers" who are suspected of murdering as many as 20 people in the 1980s and 1990s. Shermantine, who was convicted of four murders and now sits on death row, has given investigators maps to the burial sites after Sacramento bounty hunter Leonard Padilla promised to pay him $33,000 for the information.

Shermantine's partner in the killings, Loren Herzog, committed suicide last month after being told Shermantine was cooperating with authorities.

Garcia said the dogs will help searchers determine where to look next after Shermantine provided information about five separate sites where he says the victims could be buried. A sheriff's hotline for people who believe their loved ones could be among the victims being found has received more than 50 calls.