Place Without Weapons

Exploration Stage: Post Office
From: Mr. Black
Description: We need to find out where the criminals went. The criminals mentioned that weapons are prohibited in this place. Yet I presume they want to slip inside with homemade knives disguised as mechanisms. I know these kind of knives. Search for them in the post office amongst the confiscated items.
Completed: If you fold such a knife, it looks like a magnifying glass used by scavengers. But these tricks won't work on me.