I once worked with a compulsive liar. This guy was good for a few stories, but I'l tell the last one first.
He lasted about 3 weeks. Racking up a bigger insurance bill for our location than the past 5 years combined. My manager had enough, told him he was fired and why. She was pissed. She didn't even do it privately. She did in front of me and another employee. Mostly because she was so angry, but also because she wanted witness since this guy clearly couldn't tell the truth to save his life.
After, I drove him home because he didn't have his own car. On the way he tried to tell me that she didn't fire him, but gave him a one week leave so me and the 2nd employee could decide if he was fired. I couldn't help laughing hysterically for a good 20-30 seconds. I never even said anything back. I just dropped him off, and never saw him again.
That's what convinced me he really couldn't really help himself. I hope eventually he found some professional to help him.