He is killed by one of Steve's goons, and the body dropped in the middle of the road, to make it look like he has been accidentally run over.

Over the short wave radio, they send a fake message that the police believe they are closing in on the fugitive near the Mexican border, to lure Steve out of hiding.

Willie's dog catches up with the truck shortly after they leave and jumps in; he starts attacking Steve during the drive.

While the truck is still moving, Kay and the dog jump out through a door, and Willie flattens the tires with his gun.

[1] The film was based on an original script called Thunder Mountain by Dean Franklin and Charles Royal.

[3] Dick Purcell died of a heart attack shortly before he was supposed to make the film.