So - was it a legal or illegal hunt?
He had permission to hunt, but he hunted a protected cat.
Kinda hard to say since the laws of Zimbabwe are what Mugabe said they are this morning.
But by my reading of the regulations, if you moved the hunt to Texas, it would have been entirely legal (baiting, private property near national park, etc), with the assumption that the animal is considered regulated by the state (which lions are not), but exotics aren't "wildlife." But for the sake of similarity for the discussion, assume wildlife, and it all seems legit.
http://tpwd.texas.gov/regulations/outdoor-annual/hunting/general-regulations/means-and-methods