What do you mean, no motive? The motive was that his financial crimes were about to go public.
But even without that, suppose we didn’t know a motive, so what? Since when has it ever been necessary to know why someone committed a crime? It’s enough to prove that he did it, and the prosecution did that to the jury’s satisfaction. What else is required?
What’s wrong with circumstantial evidence? When has it EVER been the case that circumstantial evidence is not enough?