A recent exciting but unpublished discovery of mine was scooped by a colleague. I am a PhD student and I shared the discovery with the colleague a year ago. The colleague is a professor who came from the research group I work in. I found out about the scoop through my adviser who attended the colleague's talk about the discovery; the colleague's group did similar research that led them to the same discovery after we talked.
Obviously my adviser and I were surprised, upset, and angry. Initially after my adviser confronted the colleague about this the colleague was argumentative but eventually saw the light and became apologetic. The colleague offered to retract the paper that was accepted for publication but not published until we've published our findings (it's taken so long to publish for good reasons). However, the colleague is still pushy about trying to get at least something from their research out, but it is our judgement that any of their results would scoop my discovery.
Although I haven't talked with the colleague since this happened (my adviser has been mediating), I get the impression that the colleague did this intentionally with the hopes that it would go unnoticed by us.
So my question is this: what should I do to ensure this colleague receives their comeuppance i.e., does this deserve some sort of punitive action on my part? I haven't asked my adviser yet and any suggestions I receive here will certainly be discussed with my adviser.