No matter what you do, some people will agree with your actions everyone will have an idea what you ought to have done (but only after the fact).

My question to you is - can you resolve this in a way that will take the onus off of you?   For instance, write to the dean of the college that supposedly issued the credentials.

Request a copy of their answer go to HR/personnel of the firm. That way, you're giving benefit of doubt, HR gets enough of a warning that they should check up on this person. You've set wheels in motion but you're out of the loop.

And hopefully your stomach quiets down. Gad it's miserable (been there but not since the late teen years when a dorm floor-mate was puffing illegal substances, thank goodness!) (One Zen bottle of Tums coming your way) ET