I like it!
Making him into Diana's "Catwoman" could be cool. He doesn't want to kill Diana. He just wants to commit crimes that she must stop.
Diana may even sympathize with him. In my opinion, Diana's best rogues are always the ones who play on her compassion. Diana has to stop him, but she doesn't necessarily feel good about it.
Though much is taken, much abides; and though
We are not now that strength which in old days
Moved earth and heaven, that which we are, we are,
One equal temper of heroic hearts,
Made weak by time and fate, but strong in will
To strive, to seek, to find, and not to yield.
--Lord Alfred Tennyson--