Four members of the Mark family are found murdered in their Cedar Falls, Iowa, home, prompting police to suspect someone close to the family; the bizarre outcome shakes the townspeople and devastates the surviving members of the Mark family. It’s a modern day Cain and Abel!
I’m guessing Jerry could have collected some cigarette butts from random places along his journey to Iowa, and planted them to throw police off. If they tested one it wouldn’t match his DNA and he’d be off. (Or so he thought).