My guess is he (I only think one culprit) parked right in the driveway, quietly scooted to the door, and the rest is history.
I, too, am confused as to why the parents were murdered. Yeah. I know the theory of no witnesses, but that seems really an extreme reason. Fixation on Jayme? From where did he see/know her. He didn't just kill two people to kidnap someone he had never seen before. Unless, of course, the double homicide was meant for the parents. But, even so, why take Jayme? My mind is "going" over this case.