You need to discover that Albert Meineke is not actually mute by catching him speaking on the phone.
You can do it after the quest “Under Suspicion”, during/after the Antoine Grubic / George Danton part of the game. Albert Meineke becomes available as a tenant after that point.
1. Talk to Albert.
2. Install a camera in Albert’s apartment.
3. Eventually, he will go to the phone and start talking.
4. Click/observe him while he is talking on the phone.
5. Confront him about the phone call.