Historian Lothar Machtan argues in The Hidden Hitler (2001) that Hitler was homosexual. The book speculates about Hitler's experiences in Vienna with young friends, his adult relationships with (among others) Röhm, Hanfstaengl, and Emil Maurice, and includes a study of the Mend Protocol, a series of allegations made to the Munich police in the early 1920s by Hans Mend, who served with Hitler during World War I. American journalist Ron Rosenbaum is highly critical of Machtan's work, saying his evidence falls short of being conclusive and often falls far short of being evidence at all.^[49] Most scholarly works dismiss Machtan's claims.^[8][9][10] In 2004, HBO produced a documentary film based on Machtan's theory, titled Hidden Führer: Debating the Enigma of Hitler's Sexuality.