As in the actual case of Robert Durst and Morris Black, David kills Malvern Bump and dismembers his body. He tosses it into Galveston Bay where it is later discovered, except for the head. It's suggested that Deborah Lehrman, in a blonde wig, posed as Katie Marks so as to be seen after Katie was murdered. It's also suggested that, on the night David visits his father shortly after Katie's disappearance, Sanford Marks looks into David's car trunk. An epilogue then reads:
David Marks' testimony in his trial for the murder of Malvern Bump convinced the Texas jury that he acted in self-defense. He was found not guilty. He was convicted of improper disposal of a body and sentenced to nine months in jail. No one has ever been charged with the murder of Deborah Lehrman. Before Sanford Marks' death, David visited his father for the last time. The disappearance of Katie Marks is still considered a missing persons case.
David is shown leaning over his father in the hospital. David whispers, "I miss her so much." In the final scene, David rides down the hospital elevator singing to himself, "Every night my honey lamb and I." (This is a line from the song "Oklahoma," which Katie is shown singing earlier.) He walks out of the elevator and heads toward the door. "David Marks currently lives in Florida. He is a real estate investor."