One other suggestion. Contact your son's cell phone carrier. They will know which cell tower his cell phone was connected to just before his flight left and again shortly after it landed. Assuming this corresponds to the flight he supposedly didn't take, I think a court would very likely accept that as proof that he was on the flight (even if there was another flight at roughly the same time on another airline, I doubt any court would find it plausible that he was on that other flight).