Only a few years ago, Tuesday’s announcement that a glove believed to be connected to the disappearance of Nancy Guthrie in Tucson, Arizona, had no match in a DNA database would have been a dead end.

TUCSON, Ariz. — A Q-tip, a tissue and a pizza crust. To investigators, this seemingly innocuous trash was DNA-laden treasure, helping crack the cases of the University of Idaho murders, the Golden ...