You would have to prove they acted intentionally, though. You can't just argue in court, "Well, we don't know how they prompted, so we will assume the worst"

If the prosecution is able to prove beyond a reasonable doubt that the person gave a prompt that was intended to commit a crime, then of course we can prosecute them for that. The AI is just a tool to commit fraud at that point, and is no different than a person who uses photoshop to alter a check to commit fraud.