Why didn't he just "say" he left it out. Perhaps he did? Who knows? His fingerprints weren't on the weapon except one. But as it was his gun anyway it wouldn't be so strange anyway would it? Especially if he was supposed to have cleaned the gun afterwards? So what did he do? (1) Really leave the gun on the settle. (2) Just say he left the gun on the settle. (3) Said he shot rabbits to explain why his fingerprints were on the gun. (4) Wipe the gun clean?
Lugg,,he had no reason to remember what he did really,,,whether he did all these things or not,,as he hadn't planned anything and certainly didn't envisage what was to become.