If an account is under investigation. Would it not be frozen, so no changes may occur. Rather than closed.

Seems to me, closing an account would have very much the opposite effect of hiding evidence in an investigation. And most investigations would not even freeze it. They would just seek the historical data. Frozen would only happen if they had evidence that the money was going somewhere illegal. Or coming from. Because freezing or closing someone's account is an event that affects the person. So, a punishment before proof of a crime. Not an event done in an investigation.

And you are correct. Refusing to open an account because you are suspected of but not convicted of a crime. Would def be illegal. So the banks would not tell him that. Meaning, he has no reason not to declare bank a refused me an account without reason. As the bank cannot then say. No, we told you, you can't have an account because you are too poor. And sue him.

Also, a person being under investigation. Is not something the legal system is allowed to keep secret from the person. They need warrants etc to gain rights to see your bank details. You legally have a right to know that. So while a bank may not be able to tell the world why your bank is frozen. They sure as hell can tell you. And sue you if you claim they refused to inform you why.

Our legal system has generally evolved to prevent organizations not giving reasons for fiscal choices. Because back in the past, it was used to enforce racism and other prejudice. It's still far from perfect.

But a bank is def required to follow its own guidelines. And document those guidelines. Before closing people's accounts or making fiscal decisions about them.

While I was in the US when I worked as a bank software engineer. So the rules are a little different. The UK def has similar rules. Innn fact more limitations, as people a legal right to get the information used to make choices about them.