This issue has been resolved. This guy was unable to provide a signed message from any of the addresses found in the transaction proofs he provided. Furthemore, the real owner of the account already has withdrawn his ETC to one of the address found in one of "siemdagmaer" deposit transaction proofs he used, which he obtained by apparently phishing the original owner.

This was one of transaction this guy used as proof : https://gastracker.io/tx/0x20bc654cc14b33643eafbf9c53f54c171c6eb5d090e648788823672e5a37bafc


This was the withdrawal made after the account was restored to the original owner: http://gastracker.io/tx/0xc07b542df05eee7ae59faf1b6a5e64e5ece27fa5c9eac2322de455e1736e3aed

So... yeah, nice try, better luck next time.