According to the Churchill assassination theory, as passengers were boarding BOAC Flight 777, German agents spotted what Churchill described in his memoirs as "a thick-set man smoking a cigar," whom they mistook for the Prime Minister. This man was later identified as Alfred T. Chenhalls, Howard's accountant and portly travel companion. In addition, some have speculated that the tall and thin Howard may have been mistaken for Detective Inspector Walter H. Thompson, Churchill's personal bodyguard who had a similar physical appearance. There is an even more elaborate version of this theory that posits Chenhalls was employed by the British government as Churchill's "deliberate double" and that he and Howard boarded BOAC Flight 777 knowing they were going to die. An alternative version of this is that the British government had intercepted German messages via the Ultra code breaking operations, but failed to notify the BOAC Flight 777 for fear of compromising the use of Ultra decrypted messages. Both "Flight 777" (1957), a book by Ian Colvin about the incident, and "In Search of My Father" (1981), by Leslie Howard's son Ronald Howard, lend credence to the idea that BOAC Flight 777 was downed because the Germans thought Churchill was on the flight.