How ridiculous!! According to the relatives there was blood on the OUTSIDE of the silencer and yet he didn't bother to look at it and clean the outside before returning it to the gun cupboard? Presumably he wasn't blind and was cunning enough to move phones etc. but didn't think to rub the silencer to remove any traces of blood?

What they thought was blood pn the outside could have been paint.
At any rate he assumed they would never look for it or figure out it was used. If he was aware of the blood then he obviously assumed police would be as dumb as his supporters and not look for it and if they did find it to just assume it is animal blood. He had no idea that it would be able to prove Sheila didn't kill herself. He had no clue about drawback.
At first police were as dumb as he hoped and bought his story that he left the rifle out without it attached so never bothered to even look for it. Even after it was found police thought the only vlaue would be fingerprints. The lab came up with the argument about drawback proving that Sheila used it and coudl not have killed herself not police.