That would mean he wont be able to tell the police. And the bodies would have to be discovered by someone. How that would play out I don't know
Far better than it did. What is worse:
A) Suspect was aware of the problem claiming he received a call that is unlikely to have occurred
B) Suspect claims to know nothing, claims to have been asleep as usual at the time of the murders
Even if they suspect him there is more evidence against him in scenario A than B.
The proof he did it as opposed to some other third party was that he knew about the problem. Otherwise their main case against him would simply have been Julie's claims and the fact that he is the only one who would profit from the deaths.
If he could go back in time and not tell Julie and make the bodies be found in the morning that means the evidence against him would be that he was the only one who would profit. That still could present a problem but it is still a better situation than with showing police you were aware of the murders and having Julie rat you out.
Furthermore, if he had never intended to pretend he received a phonecall he could have shot both parents as they slept. He might have been able in that case to have prevented Nevill from reaching the kitchen and the fight from ensuing. The fight helped implicate him in several ways including that had Sheila beaten Nevill then she would have had medium velocity impact spatter on her body and clothing.
Consider how much better Jeremy would have been if the following happened:
1) Jeremy managed to immobilize his parents so that there were no struggles
2) Jeremy never told Julie anything so she could not rat him out
3) Jeremy removed the moderator and left it near Sheila's body and killed her without it attached
4) The next morning he and others say something is wrong because the door is locked from the inside and no one will answer so with the help of others he breaks in and they find the bodies then call police.
What is the evidence against him?
1) the evidence of no GSR on her hands or clothing is the main evidence against her not having shot herself or loaded a rifle. If he made her lay down when he shot her and held the gun close across her body though he would have gotten soot and GSR on her gown so even that could have been taken care of with good planning and we are using hindsight afterall.
So the physical evidence that suggests it wasn't a murder suicide would have been substantially more limited and probably not enough to even warrant a trial let alone to result in a conviction.
