Exposing a 'stolen valor' fraud...

Ok, so I've recently been introduced to a guy that I'm pretty sure is lying his arse off about his military experiences. He is about 50 years old, decent shape for an older guy so my doubts don't stem from physical features. I've already caught him lying about work and women 'achievements' so I know he'll embellish events to say the least. What grinds my gears is that this dude makes it sounds like he's Chris Kyle. Confirmed 39 kills, secret missions, outrageous situations that he'll revert to 'I don't want to talk about it' when pressed for details, etc. Tonight, he stood up in front of a small group and talked about how he killed his first human at 18 years old and the memory and pain still haunt him blah, blah, blah. He introduces himself to new people as 'Gunny" because supposedly that's what he's been called all these years. I refuse to call him that but whatever...

So, how can I prove this guy to be a fraud? Is there a website or anything that has enlistment dates or awards or anything like that? Other than asking where he went to boot camp and shite like that, what can I do to positively out him?

I have to do something to end this charade and call bullshite on this jackass.