It never ceases to amaze me that employees when caught and being disciplined get all out of kilter and decide that they have not done anything wrong. Defiance and Destruction become the order of the day. Everything becomes a fight with the person being accused of wrong doing getting more and more abrupt as they have been caught. Why not just admit what you did was wrong and (sometimes) quite literally move on.
If enough proof is offered, why not accept that you have erred, learn you lesson and move on from this?
Every day brings new challenges in HR and every day brings something new, great for keeping going and learning all the time.