Call Arnie K directly & explain the situation. I had the unfortunate experience of doing just this 7 years ago. I had sent in a LOR for a buddy who I had no reservations about, I thought he was solid. Turns out he'd been fired from a job, multiple checkride failures and had been arrested by the DOJ for Immigration fraud. I was dumbfounded when I found out and felt betrayed. I called AK and explained the situation and apologized prophetically. AK thanked me for the update, appreciated my integrity for the tough call and succinctly said that person would be blacklisted from ever interviewing at DAL. I have since recommended 2 others who've both been selected. Had I not made the first call subsequent candidates that I wanted to recommend may have been tainted.