Yeah, it looks like Nexon was trying to crush their competition (there was a lead developer that left Nexon and went to work on Dark and Darker).
The police didn’t find anything obvious when they investigated Nexon’s allegations. And they had already had an audit conducted by an external group:
Our code was built from scratch. Most of our assets are purchased from the Unreal marketplace. All other assets and all game designs docs were created inhouse. This has already been audited by an outside agency. As far as we know you cannot copyright a game genre.