It may be pointless resigning as you would be unlikely to get another job easily with this matter in hand.
You don't tell us if you did not commit fraud against your employer. If you didn't then an investigation may prove you innocent, which is the outcome you need to be working towards. Attempting to resign during an investigation could imply guilt in some people's minds, and that is something you need to avoid if you are to salvage your future career.
The only people who can help you are your employers. None of us work for your bank, so we have no idea what is in the management's mind on this matter. Your first action is to initiate a discussion with senior management since you are still employed and being paid. I suspect you would have been fired instantly if there was no doubt in anyone's mind about your part in this sorry episode.