Given the placement of the silencer when it was found, it doesn't look as if it was just 'put' in the cupboard. To place it there required some effort. He may have thought it wouldn't be found. He may have thought that if it was found, because of it's placement, it wouldn't be seen as having been part of a crime. He MAY -temporarily- have had some thoughts about retrieving it later to dispose of, but as so often happens after great efforts, he may have become drained of "try" and convinced himself that it wouldn't be found.
I don't believe any of that. I don't think he would let them go through the house if there was anything at all to find. I just don't get why he would allow them to go into the house at all. They got the safe open and everything. They also removed guns.
If he was not guilty, I might think that he was sick of the thought of going in there and didn't care what the relatives did, but I don't get why he would let them in if he was guilty.