We don't need AIs to achieve this level of self-directed autonomy free to engage in criminal behavior without consequences: we already have Employee Handbooks.
Is that illegal though? I mean, I can create an account for you on my web platform, and everyone else.
And that's what WF did: https://en.m.wikipedia.org/wiki/Wells_Fargo_account_fraud_sc...
And if the AI manages to actually assert control of property on its own, it is no longer a market actor, it is a revolutionary army.
But for the person who created the entity, losing the company is a better outcome than going to jail.
"who would be held responsible?" is still pretty easy here. by default, if you own or release to the public a system that ends up hurting someone, you are liable. it doesn't matter what your intent was or whether there was any way of knowing that the bad outcome would happen. the only way you can get around this is with "safe harbor" exemptions. it's possible that your blank slate would qualify, although you would probably have to lobby for this before the fact. in that case, no one would be held responsible. otherwise, you would be paying.