Basil Cock was the executor of the estate. What was he doing there with people who weren't beneficiaries?
If you had murdered five people, had your version accepted, and been left to it, would you not lock the house up and not anyone in?
David Boutflour said he went there to help his sister tidy up and to try to glean any information about the tragedy. He said Mr Cox arrived later.
It sounds very much as if, job done, Jeremy simply b******d off. As you say, HE was the beneficiary, but there were things which needed doing which he'd surely have been needed to oversee, apart from which, there was a family in shock and grieving, and probably not knowing what to do. Irrelevant of his feelings for them, it would have been courteous to be there with them, and some indication of what he was planning would have been useful.