Patty Vaughan disappeared on Christmas Day 1996 in La Vernia, Texas
The mother-of-three, then 32, was last seen by estranged husband J.R. Vaughan
He claimed they had an argument and she stormed out of her house
Patty's minivan was found the next day, with blood inside and a deflated tire
Her body has never been found, but authorities presume she is dead
Investigators say J.R. is a suspect, but no charges have ever been brought
J.R. later left the state with their children and has since changed his name
He has always insisted that he was not involved in any foul play