The Nancy Guthrie investigation could hang on a strand of DNA

One hundred days is an agonizingly long time for a family to go without answers about their missing loved one. It's also long enough for the investigators working the case to feel the grind. At the 100-day mark, the investigation into the disappearance of Nancy Guthrie could hang on a strand of DNA that's still being evaluated by scientists at the FBI laboratory in Quantico, Virginia, in hopes of identifying her abductor. Guthrie, the mother of "Today" show co-anchor Savannah Guthrie, was reported missing Feb. 1. The DNA recovered from Guthrie's home in Tucson, Arizona, was first sent by Pima County sheriff's detectives to a private laboratory in Florida for analysis. Weeks later, the DNA was shipped to the FBI's state-of-the-art crime lab in Quantico, where law enforcement sources tell CBS News the work is ongoing. Investigators have not publicly confirmed details about the sample or exactly where it was found. "An item containing DNA such as a strand of hair found somewhere in a house is one thing, but a strand of hair near the victim's last known location, such as in her bed, would be a high priority for the FBI," said Lance Leising, a former FBI supervisory special agent in Arizona. The painstaking process of DNA analysis , including building out family trees, doing forensic comparisons and elimination work "takes far longer than television crime dramas would have people believe," said retired FBI Supervisory Special Agent Jason Pack. …