Rent/Signature Fraud Doubt

This is in continuation to this. Please share your opinion. Thank you https://www.reddit.com/r/LegaladviceGerman/comments/1osj74w/comment/nnxkciu/

Addition - I found the proof that the signature is fake/forged, infact the whole contract that he gave me is fake written by him. Landlord is probably not even aware of it. While vacating the apartment, he also asked me for additional money saying "landlord is asking for it" - this probably was also a lie.

Do I now have a good basis to sue him for signature fraud and rent fraud?