I don't think by naming that person I will prove anything. He is not directly to blame, most of this is on us.
What? He deliberately added code to cheat your players.
How is he not to blame?
You're to blame too, for putting his code live, but he's also to blame for writing the malicious code! How is it fair for him to do this and remain anonymous? Someone else might employ him and get fucked over in the same way.