What Could be the Causes for Rabbit's Death?

At 10:30 AM, a cat was about to get a rabbit on the lawn, while my husband chased the cat away. However, the cat must have attacked the wild rabbit before we saw the cat's continuous action. My husband took his white shirt off to cover the rabbit, so it wouldn't run while he brought it to the garage to check if the rabbit got hurt. The white shirt got blood stain, so we knew that the rabbit was bleeding. It seemed that the rabbit only got one 1/4 to 1/2" wound on its chest. It did not look serious and no blood came out. I put peroxide to disinfect the wound and the ointment for cut wounds.

We put the rabbit in a deep box with water, celery, and lettuce. We planned to keep it and check the wound, and release it to the wild once the wound starts to heal. The last time we saw it alive was about 10 PM. It did not touch the vegetables yet due to its trauma I guess.

This morning, we saw it laying its side-way dead. No blood was found. It did eat some parts of the vegetables. I don't understand why it died. If it was able to move and hopped around and ate, the wound was not serious at all... Why... Did we do something wrong??? It's only one night...