Couple things regarding this:
Was there an exchange of items prior to spycrabbing? If so, you'll need to provide some evidence of this as well, normally in the form of a screenshot of your trade history.
If not, then this kind of gambling is not something we police. My opinion on this is: no items were exchanged, so no parties were hurt. However, I believe SteamREP processes these kinds of "scams", so you can try reporting it there.
I would assume that no items were exchanged because the screenshots show that Demopan owes him 1 key + 2 ref, and Demopan would've probably ran instantly if he had the items and he lost so that he could gain the items.
At OP, if you tried to report it to Steamrep, I'm not exactly sure if they would accept it since it's basically like chat logs when trying to report a scam. Next time you spycrab, record the whole entire game, and have the pictures/proof that says that both parties agree to the spycrab, while also stating the rules before you agree so they can't use the excuse of "Oh, I didn't know the rules." If you get all that proof, you'd have more then likely a chance to get him marked for Spycrab running.