Just my opinion but I think the killer came well prepared. He knew exactly where the phone lines were and was able to cut them in the dark. It also appears he knew exactly where everyone was sleeping, probably because he had previous scoped out the house. He was able to quietly enter and execute the parents without waking the other. After all, the house was up for sale and there had been several open houses. He probably showed up for the open house, walked through and was able to tell exactly which room was Jennifer's and which was the master bedroom. He may have been aware that on hot summer nights Michael would sleep in the garage. (the garage door was found open). He appears to be a meticulous planner. I think he may very well have been the person sitting in the truck that was observed by the witness.