After you have gone through getting past Janosch (Liebold's remote) and meeting your future self you are faced with the Unorganized Crime. You would have to get rid of Nod and Wink and get the gun.
This is the low-spoiler guide for "Hostage situation" puzzle in Chaos on Deponia. Unlike in normal walkthrough, you get gradual hints on how to solve the puzzle. Click the big button below to see your first hint. If the hint contains a spoiler, you will be warned about it before clicking.