Trivia: Before getting the role of Walter Donovan, Julian Glover had auditioned to play Colonel Vogel.
Trivia: Kevork Malikyan (Kazim) had previously auditioned for the role of Sallah in "Raiders of the Lost Ark" (1981).
Trivia: Vogel's name is never spoken in the film. It is only mentioned in the closing credits.
Trivia: Despite his prominent billing, John Rhys-Davies does not appear until 53 minutes into the film.
Answer: Henry says, in response to Indy asking if he remembered the details of the trials: "I wrote them down in my diary so that I wouldn't have to remember." So, obviously he did NOT know them by heart. Also, as the other answer says, they didn't want the diary to either be in the Nazis' possession or be burned.