In my country, we can buy pre-paid credit cards in the supermarket using cash. I guess that is still traceable using supermarket security cameras and facial recognition, but if you're attempting this, I'd make it as difficult as possible.
Maybe. If they can identify which record was the last one changed and the last one changed its directly related to the one that made the change and the ended transaction statement successfully posted a transaction
If the SQL injection crashed that person's transaction there's little chance of finding the culprit