Ain’t do no wrong

I’ve seen this multiple times but never understood how it’s correct.

I think it should mean - He didn’t (ain’t) do nothing wrong = he did something wrong?

There is barely any evidence in the case. They are literally trying to dig up on him but there really isn’t much to find.

I’m not supporting him saying this but there is no denying that there is minimal evidence and that he has been treated unfairly, by the judge and by the media. You are innocent until proven guilty.