As a historian, cultural anthropologist, UFO researcher, author and film producer I investigate the Carlos Diaz contact case for seven years. Since I wanted to be sure before I publish the case that any possibility of a hoax can be excluded, I did not only travel to Mexico twelve times for on-site field investigations, but also consulted leading experts in the US, Belgium, Germany and Italy, including * Prof. Corrado Malanga, University of Pisa * Prof. Manfred Kage, University of Mannheim * Prof, Auguste Meessen, University of Louvain * Bob Shell, editor "Shutterbug" Magazine, phototechnical consultant of the FBI * Dr. Robert Nathan, Jet Propulsion Lab/NASA, Pasadena * Jim Dilettoso, The Village Labs. None of these photo technical experts found any evidence of a hoax in the films and footage shot by Diaz. Field investigations were performed also by Prof. John E. Mack of Harvard, who spent three days in Tepoztlan and extensively talked to the witness, his family and local eyewitnesses. We were able to verify that over 50 % of the population of the city of Tepoztlan, in which Diaz lives, about 12.000 people, saw the very same type of object filmed and photographed by Diaz, a fact confirmed by the mayor of Tepoztlan. The Air Traffic Controllers of Mexico City's International Airport confirmed on camera regular UFO sightings over the area of Tepoztlan. Several researchers who visited the place, including Dr. Roberto Pinotti, saw the very same ship Carlos filmed and photographed.