I'm surprised the bunny survived the initial cat attack; rabbits are notorious for dying of heart failure even just from fright. When I was in my 20's, my grandfather asked me to hunt some rabbits at his acreage with my .22 as the property was being overrun by them, and they caused a ton of damage to their large fruit & vegetable garden. I shot a lot of rabbits, but one of them died just from the sound of the gun. I shot & missed it, but there the body lay. No bullet wound whatsoever, it just keeled over and died of fright.