From what I can see there is no storage centre of screenshots for anything to do with this beyond the publicly available evidence chest, though maybe I just haven't delved deep enough into the lair of evil.

My position on screenshots for the record is that if they demonstrate an intent to break the rules of the site, then yes they should be used as a source of evidence to justify a warning or ban. Therefore I suppose if you felt the screenshot of a private conversation constituted some sort of abuse of power it would be understandable why you did it but don't be surprised if the person involved in the discussion is less than receptive to having private conversations screenshotted.

If that view makes me a hypocrite then you have no idea the meaning of the word.