(Salt Lake City-AP) -- An investigator says they were compared to 84-thousand other sets of fingerprints that were on file -- including those of Brian Mitchell, the man who's now in custody in the case. And there wasn't a match with any of them. Kevin Patrick says it's been a "frustrating" search. He's a criminalist at the Utah Crime Lab -- where for the past nine months, one person has been working exclusively on the Smart case. At least 15 others have also taken part in the investigation. Patrick says in a high-profile case, it's unusual for his staff not to be able to match a set of prints -- but it does happen. He says his staff tried to get a full set of Elizabeth's fingerprints so they could be sure the unidentified ones weren't hers -- but they were only able to find prints for eight of her fingers.