don't just let it go... I'd try to reach out to them and at least see how they react when being told about any suspicions one might have!

It's the community that creates the ethical framework by their actions... just letting things slip by, imho, is not healthy for the bigger picture.

But I know how it feels... I also hesitated contacting anyone... putting myself in the spotlight as the accuser and all that... I really had to make sure I can back all my claims up should anything appear questionable about my findings.