the two shots to Sheila are contact shots Snow and there is no evidence the silencer was on the rifle when she was shot. So whether JB is guilty or innocent Sheila's blood should no have even been in the silencer.
If Bamber leaves the silencer beside Sheila in a area of high blood flow he is home and dry in my view. If he leaves it in the cupboard he gives it a dam good clean first! and to make sure he does not let anyone have the keys to the house!
This isn’t about being “home and dry”, it’s about rushed decisions, in the heat of the moment and not forensic perfection. Panic doesn’t allow perfect decisions and Leaving the silencer out would draw attention, putting it away nearly worked for him, and the minute trace blood found fits rushed judgement.
The Keys were allowed to be given to Anne for cleaning purposes, this was vital for Bamber, it would mean evidence gathering was done with, and the investigation within WHF was finished and Bamber would have hated cleaning up after murdering his entire family.