We have gone through this.
Who an earth would break in, massacre men, women & children & not take anything.
If Jeremy is innocent, how did Sheila commit the massacre.
If Jeremy just shot Sheila (twice) and left it at that, left a door open, hadn´t invented the call from Nevill, thus not calling the police, the case would be open.
As it was, he preferred to stage a two-shot murder as suicide, paint himself into a corner with the invented phonecall, call the police and face the music, blurting out how he disliked his sister.
Something is terribly off in that scenario.