gebirg - That is a Mauser WTP I, or first model , 3 type/variation. Defined by a single grip screw and the "MAUSER WERKE..." slide address. Thank you for sharing the info on its capture.
How did you determine the holster is for a Walther model 9? I would not think a WTP I would fit in a holster designed for a model 9.
Regards,