The guy had many, many aquariums they found when they searched his home. They say it was almost as big as the public aquarium he stole from. My guess is that he wanted the shark for his own personal aquarium. Anyway, they got it back and it lived, so there's that.
At first I laughed, but as I read on I got a nasty feeling creeping up. These guys killed a shark, and it was a fucking traumatic end to its life.