There was no proof that Vader bit someone. An anonymous phone call, a picture, and a claim that is almost impossible to be true.
The second bite was true, though. He bit the officer because the officer ignored Vader’s owners offers to crate him and warnings not to grab at him. The official report said that Vader bit through the gloves, but a lot of people with experience with foxes have testified as to how unlikely they were due to the high grade of the gloves.
But that’s not even the point. The point is that people keep defending his death by saying “his owner wasn’t supposed to have him!” which is a complicated issue in and of itself but entirely irrelevant to the events which unfolded that night.