ANTIOCH , California ( CNN ) -- Investigators found another bone on property belonging to kidnapping suspects Phillip and Nancy Garrido on Friday , as they scoured the yard for possible clues to the abductions of two other girls about 20 years ago , officials said . Police search for evidence relating to missing girls Ilene Misheloff and Michaela Garecht . At an afternoon news conference , authorities revealed that the bone was discovered as crews broke up concrete on the property . Hayward police Lt. Chris Orrey said it will take time to determine whether the bone came from an animal or a human . The search Friday at the property in unincorporated Contra Costa County involved the use of ground-penetrating radar , which showed irregularities in an area of the yard where cadaver dogs working separately showed interest Thursday , investigators said . See how ground-penetrating radar works » . The Garridos face a combined 29 felony counts in connection with the 1991 kidnapping of Jaycee Dugard , then 11 , from South Lake Tahoe , California . Authorities say the couple held Dugard in a hidden compound behind their home for 18 years and have said Phillip Garrido , a registered sex offender , fathered her two children . Police from Hayward and Dublin , California , on Tuesday began executing search warrants simultaneously on the Garrido property and an adjacent property that he had access to . They are seeking any evidence in the 1988 abduction of 9-year-old Michaela Garecht of Hayward and the 1989 disappearance of 13-year-old Ilene Misheloff of Dublin . Both agencies have said that , although Garrido has not been named a suspect in either case , he can not be eliminated as a suspect . Orrey said `` boxes and boxes '' of writings by Phillip Garrido were also recovered on the property and were being taken off-site so investigators `` can look through every single page . '' Little work will be conducted at the site over the weekend , Orrey said , but investigators will remain on the property to ward off trespassers , who have been spotted there in the past few weeks . When the search resumes Monday , two kinds of search dogs will be brought in , authorities said : cadaver dogs and archaeological dogs . Cadaver dogs detect decomposing matter , investigators said , and archaeological dogs search for older material . Earlier Friday , Orrey said the dogs would not return to the area until after it was cleared of debris . `` We just want to have all of the areas clear so they can do another sweep of the entire properties , '' she said . Authorities also plan to continue searching the Garrido house , which county building inspectors have condemned as unsafe to occupy , Orrey said . On Wednesday , authorities said they had found bones on both the Garrido property and the adjacent property but did not know whether they were animal or human . Another bone fragment was found on the adjacent property last week .
NEW : Radar shows irregularities in yard where cadaver dogs alerted . NEW : Another bone found as crews broke up concrete on the property . Phillip and Nancy Garrido are accused of abducting Jaycee Dugard . Ilene Misheloff ,13 , went missing in 1989 and Michaela Garecht , 9 , in 1988 .