Jeremy is supposed to have had the nerve to shoot everybody, his last victim twice to make it look like suicide (!), "hide" the silencer with blood, paint and a hair on it, cycle home, hide his clothes (where??), wash up, put on fresh clothes.
Then call the police to create an alibi, which wasnt really an alibi, but still, hey ho. Meet up with police outside the murder scene, confident they would not be looking for any clues of murder, since he nudged them in the direction that his sister, whom he had shot twice, was a nutter and had gone crazy with a gun.
Confident they wouldn´t suspect him when they found her with two bullet holes to her neck, confident they would not look for the silencer in the house, wouldn´t look for possible footprints or other traces of him (for instance outside the window he is alleged to have exited through), wouldn´t search his house containing bloody clothes.
All of this does not make much sense to me.