Three young males drove 50 miles to go to the zoo on Christmas day- when it would be practically deserted. They wait until the zoo closes to approach the tiger. The kid that got killed had no id on him. This whole thing was preplanned. It was either some kind of initiation or it was a “jackass” inspired stunt. In fact, I’d be willing to bet this is a dare type thing that has been done before at this very same zoo and is known by kids in the area. They antagonize the tiger by throwing rocks and sticks at him. Then they stick their legs over to show how brave they are with the tiger jumping up at them. In fact, I wouldn’t be surprised if more than one of these young men took a turn at it that day.
It is all Bush’s fault. :)
Your scenario is starting to add up. The moat is apparently quite shallow, designed mostly to keep the tiger from getting a firm footing for a leap and scramble up the wall rather than to actually deter crossing.
Several posters have mentioned rocks and branches being thrown into the moat and someone speculated about a park bench or something similar being tossed in.
If the three victims put enough stuff in the moat, the tiger could have jumped onto the wall, then scrambled high enough to grab Sousa’s dangling leg, which would explain his shoe being found inside the enclosure. It could then have scrambled over, arresting his fall and pulling him back to the outside of the wall in the process.