We have to remember that DS was reported to LE as a missing person possibly due to a medical emergency. If LE rolls up and does not initially see signs of a struggle or any blood, they probably thought there's no reason to take fingerprints. Do I agree? No, but Idk if Sac County deputies are rolling around with fingerprint kits in the cars. Also, SS had her son and his girlfriend clean the truck out shortly after DS went missing, so if there were any prints, they were probably destroyed or not usable.