Not to downplay what happened, but you're probably best off just moving on. The animal already gave you enough headache and wasted enough of your time. The time, effort, brainspace, and emotional health, along with the slight chance of the employee actually getting fired, do you really want to give this one more second of ur time? Unless you have extreme concrete proof, and maybe have an attorney threaten legal action, it's very unlikely the employee will be fired. If you move on, you will be doing urself the biggest favor.
Wishing you all of the best either way.