What would you do if a relative who had just got out of jail moved in with you and made your family's life unbearable? And what if you and your wife accidentally killed him? And what if a neighbour's son saw you trying to bury the corpse in your backyard? And then, what if a traffic cop happened to notice that suspiciously quiet relative in the back of your car?
You wouldn't really want to spend the rest of your life behind bars, so you'd probably start by getting rid of the body... and the young witness too, no doubt... and you could hardly afford to let that policeman talk about that not-quite-living guy and random kid he found in your car...