I don't understand your reasoning. WHY would he hang around after he'd killed everyone? SURELY the most sensible thing was to put space between himself and the soc -which he did- and use a fictitious phone call from his father as proof he was at home NOT at the soc......................which he also did?
Your approach is all wrong - how could Jeremy force cops to report two bodies downstairs, from 7.37am, and the other three bodies upstairs at 8.10am? Why did the occupants of CA07 who were responsible for 'relaying' information received from inside the farmhouse at 7.37am, 7.38am, and 8.10am, to the control room at far away Chelmsford police station, choose to stay silent, in the knowledge that by the time the case came to trial in October 1986, the body count downstairs and upstairs, was different to 'that' reported by them up to, and inclusive of 8.10am...
Odd that...