Fingernail clippings taken from a murder victim in 1982 helped Phoenix police make an arrest in the killing last week, after tests confirmed that DNA found under the victim’s nails matched that of a convicted sex offender, the Arizona Republic reports.

The arrest was the latest in a growing file of Valley murder cases once considered unsolvable. Advances in forensic technology have allowed scientists to test miniscule bits of evidence and match the decades-old material with suspects.

Karen Casanova, 28, was found in a vacant field near 20th Street and University Drive at about 5:45 p.m. on Jan. 31, 1982. The body was partially clothed, and investigators determined she was sexually assaulted and smothered, according to court documents, but there were no witnesses and few clues.