The police offered the keys to Jeremy after they had finished their investigations and he declined them and suggested they gave them to AE, why would he do that when all he had to do was take the keys to his house and walk in through the door, lock it behind him and tie up all the loose ends he needed to. Doubt he'd give away the keys wait a while then climb through a window one night to retrieve the silencer.
If he entered WHF through the bathroom window, after his first holiday, that is very suspicious. As no one saw him enter WHF before his first holiday to Amsterdam.
He would not be aware the silencer was at the lab. But was aware that he was coming more under more suspicion.
As my previous thread said, there was no reason the police would find the silencer within the first three days. However a second search...