The Disappearing Money

In the Colorado mountains, a large sum of money disappeared from a crashed plane. Years later the money has not been found and there are no suspects. Detective Marcus Rothman, a passenger on the plane, takes his girlfriend for a week's vacation to the Colorado mountains where the plane crashed, and they do a little searching. By pure luck they find one of several suitcases of money. Before they can turn it in, it disappears. Can he find the missing money, and who took it?