I'm curious how big the bank was and what country this is in?

It's my understanding that banks really don't want your money once they've closed an account, they want you to take it back.

Bigger banks, at least in the US, usually do this.

I am guessing it's not that they wanted the money. They thought there was something illegal happening and seized the money. I.e. not for themselves but for whatever law enforcement agency they thought might come looking for it.

If they thought you were money laundering, maybe giving it back would be a liability.