The only authenticated photograph of the infamous Billy the Kid was auctioned off this weekend in Denver. The auction house expected the photo to sell for somewhere in the ballpark of $300,000 tp $400,000. Instead, Florida billionaire William Koch won the photo with a bid of $2.3 million. We talk with Mark Lee Gardner, author of “To Hell on a Fast Horse: The Untold Story of Billy the Kid and Pat Garrett,” about why we are still fascinated with the Wild West gunslinger, more than 100 years after the death of Billy the Kid.