Updated

Authorities investigating two missing girl cases said Thursday that cadaver dogs picked up a scent that could indicate buried remains in the backyard of a Northern California couple already charged in a kidnapping.

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Alameda County Sheriff's Department spokesman Sgt. J.D. Nelson said two dogs "indicated" on a site in Phillip and Nancy Garrido's backyard. But he cautioned that the area is known to have buried remains from Native Americans and animals.

The Garridos are charged with the 1991 kidnapping of Jaycee Dugard, who was snatched outside her South Lake Tahoe home when she was an 11. Prosecutors say the Garridos held her captive in their backyard for 18 years. The couple has pleaded not guilty.

Since the Garridos' Aug. 26 arrest, their California home has become a focal point of investigators reviewing outstanding kidnapping cases in the San Francisco Bay area. Their lawyers are not discussing the property searches.

Authorities are seeking any evidence on the property that may link the Garridos to the 1988 abduction of Michaela Garecht outside a market. Police are looking for clues that may tie the couple to the 1989 disappearance of Ilene Misheloff.

Nelson would not say where in the yard the dogs picked up a scent and warned of false positives.

Investigators planned to use high-tech radar equipment to scan the site on Friday. They would start digging if the radar gives more specific information about what is underground, Nelson said.

Cadaver dogs are trained to sniff for the scent of a decomposing body and can catch smells of up to two or three feet (one meter), Nelson said.

"They picked up a scent that may or may not be a sign of some remains," Nelson said. "The first dog was very tentative on its indication. The second dog was more direct and indicating directly."

On Wednesday, police recovered a bone fragment on the Garrido property and several more in a next door neighbor's yard that also was being searched by investigators because Phillip Garrido had access to it.

Tests are being done to determine if the bones are human or animal, officials said.

Investigators continued clearing trash and brush from the backyard that was outfitted with tents, sheds, an above ground pool and showers, and have collected personal items that they wouldn't identify that they say belong to Dugard.