There's going to be evidence of the stuff they threw in the cage. Some might even have finger prints on it. Then their will be finger prints on the bars where the kid(s) went over. Those prints will be facing the wrong way and appear above hte blood spatters on the inside of the cage wall. They'll also be cat scratches on the wall, where the cat went up.
The zoo will be able to show the cage was good enough for normal holding, but not for holding a taunted animal. These morons were yelling and tossing stuff at the cat, thinking the cat wouldn't be able to respond. I don't see cat cage engineers considering that scenario. Any lawsuit should be dismissed as frivolous.
I’ve read reports there were witnesses to at least some of the taunting.
It will make a good case to fictionalize for the CSI TV show.