I was at the office one night kinda late, and I walked around the corner to see him working on the server. He was installing what looked a lot like a graphics card. Sure. Not mining.
In the end, he never got caught. I recently looked him up on LinkedIn and he hasn't been working for over a year. I obviously don't know this for sure, but given what a bitcoin enthusiast he was, I would not at all be surprised if he made a fortune mining for free by stealing the company's money and also investing heavily.
Indeed, greed in cryptocurrency is a thing.
(Created a throwaway to protect the privacy of the guilty, even though they don't deserve it.)