I mean, one of the biggest things I can't figure is that there are apparently 2 driverless cars in play, Krista's and the other one that was impounded. The killer could have followed her from Portland and abandoned the car -- but then how did he get out of North Conway? It's not exactly Grand Central Station!
Maybe the baby's father's car? He likely had a vehicle before going to prison and maybe it was parked or used by a friend until he is released.