Are various aspects of your employer's defense reasonable? Are various aspects of your employer's allegations against you plausible? It sounds simplisitic, but this is a big deal.
Really read through complaints made about you by your employer and ask yourself if a third party (read: a lawyer or investigator) will find inherent plausibility in your employer's arguments. Is what your employers are saying about you sound on its face?
Here's what I mean. In an effort to retaliate against me, for an issue I won't go into here, my employer accused me of being disliked by all of my coworkers. Yes, I mean every last one of them! However, just 9 months earlier, my employer gave me a written evaluation that stated I was a joy to work with, was pleasant, was well-liked, etc. So, instead of it being my word against my employer's word, my final year-end review showed there was no inherent plausbility to my employer's argument that every action taken against me had to do with the fact that I was intensely disliked and, therefore, was disruptive on my projects.
You need to read every sentence of important emails and documents and highlight what arguments/defenses are cleary implausible. This will help prove your case, may show that your employer is engaged in a coverup to hide the true motives behind their actions, and can be the key to establishing your credibility with any third party that becomes involved in your case.
Show how your case is plausible and truthful, while showing how your employer's defense and arguments are completely without basis and unreasonable.