Did you owe him the rest of the fund? No, I don't think so.
Did he have to return the 2btc? IMO, no. It's his reward for finding a loophole and the consequence you have to pay for not screening your program thoroughly enough.
Did he deserve a type-2 flag? Again, IMO, no. A red trust maybe, but not a flag, as he didn't breach any contract. He's not a member of the test program under contract, nor your TnC --as he stated-- specifies that betting negative is not allowed.
Oh really? Based on your opinion. If you go to a shop and see no one there is even no shopkeeper. would you grab anything you want and run away? And do you think that it's your reward and you should not return it to the shopkeeper because it's his responsibility to secure and keep eye on his shop? Should shopkeepers advertise that stealing from their shop is forbidden? If he doesn't do. That's means stealing from this shop is okay. Right? If yes, then he doesn't deserve a red trust too. He deserves to be DT-1 and he should be on everyone's trust list. I was wondering how the heck people do looting from a chain shop and who are these guys? Don't they feel it's not right? I guess I found some guys like these.
Anyways, Not just did he steal 2 BTC but also he was back again and making complaints that the casino is not paying. They blocked him. He is trying to blackmail the casino. That's why we are here with an accusation after 2 years.
My opinion doesn't match your illustration. Your illustration tries to paint the thief's morality, i.e.: should or should not someone steal when there is a chance, while my post --which even more explicitly stated on the post above it-- already acknowledge that he is cheating, my post is about responsibility.
If we have to use your illustration, do you honestly think the shopkeeper is completely not at fault and could not be held responsible to certain degree because he leave his store unattended and some stuff is lost? "
it's his responsibility to secure and keep eye on his shop?" uhh, yes? Doesn't it a shopkeeper's job to keep the shop? It's in the name, "shop-keeper".
Likewise, it's the dev and security team's job to make sure their platform is secure and bug free. Thus, a beta test and test net and security update. One thing that zi amnnot shy away to say, if you need to hear them, your team is good --and lucky-- enough to notice the bad transaction when he tried to withdraw 2btc and prevented him from taking further damage. But what is done is done.
Let's revisit your thief illustration. Have you encountered a scenario where a thief return the stuff they stole because he's asked to? I haven't. Thus, my three conclusion as above post:
1. You have no responsibility to give him the rest of his "money" because he's blatantly cheating.
2. He doesn't have to return the 2btc he stole.... which seems angered you, so if I may rephrase to better suit your situation, the atatement I said before can also be read as, "team shouldn't expect him to return the money, it'll be easier to consider it as a dead-end, because there's no chance he'll return it."
3. The type-2 flag also didn't match the situation. Type-2 flag is for a breach in an implied contract. You have no contract with him and he didn't break an TnC on your site. He stole. If you want to judge this user better and fairly, a red trust and type-1 flag --or is that yellow flag is type-3?-- suits better.
Besides, let's say we support the flag and it's activated, what benefit can be achieved from raising type-2 flag to his account? His account is a newbie account created 5 days ago. If it's tagged with flag, all he need to do --which I am sure he'll very likely do-- is just disposes off the account. The point is, you're pursuing a wrong path. If you want to contribute more to the community, the casino community to be specific, and punishes his for his action, it'll be better to share something more permanent and personal like his IP address --not a techie here, so I'm not sure if it's something permanent or we can change them easily like telegram username-- so that all other casino could put him on their ban list. Not sure if it's allowed by the forum to write them here, but I very faguely remember that some people shared a cheater's IP. And suppose it is not allowed by the forum rules, there's a specific board on this forum that allows personal information to be shared, it'll be a safer bet, if you really want to contribute to the gambling society by ridding a cheater.
Now, that's all about return, payment, and flag-related-cheating. As for the blackmailing, it should be another situation. What's his blackmail looks like?