Three weeks after Nancy Guthrie was abducted from her Tucson home, investigators have revealed that DNA recovered from gloves found near the scene does not match DNA located inside the residence. For some following the case closely, the update felt like a setback, but forensic consultant Dr Ron Martinelli says it should not be viewed that way.
Dr Martinelli explains that DNA recovery from gloves depends heavily on how they were removed and whether biological material was preserved inside. 'You're going to get the DNA from inside of the glove, not outside of the glove,' he says. 'It really depends on how the person removes the gloves.' If latex gloves are pulled off inside out, the interior where sweat and skin oils are present may be better preserved.
He notes that even if initial testing did not produce a match, advances in forensic science mean evidence can continue yielding results long after it is first collected. 'You're starting to see now cases that are 30 years old that could not be solved before are now being solved because they're running the cold case DNAs through the new DNA technology,' he says.
Beyond standard DNA comparisons, Dr Martinelli points to the growing role of genealogy databases in modern investigations. 'With genealogy, you may not get the person, but you're going to get a relative of the person,' he says. He adds that the key step will be ensuring any viable DNA is submitted to the FBI's CODIS database.
Dr Martinelli also addressed questions about why the sheriff's office contracted with a Florida lab rather than using a local facility in Tucson. 'A lot of times you don't go with your local state lab because they're so backed,' he explains. 'Municipalities contract out all the time.'
While the DNA findings are still developing, Dr Martinelli's broader concerns about the case remain unchanged. 'It still worries me. It still concerns me that we've had no proof of life after this many days,' he says. He also notes that reported communications have not come directly from the alleged kidnappers. 'No proof of life, no direct contact with the kidnappers. To me that's worse.'
