 He collaborated with Federal Bureau of Narcotics Director Harry Anslinger on the article "Marijuana, Assassin of Youth," which originally appeared in "The American Magazine" in July 1937.Some of Cooper's correspondence with Hoover is archived at the University of Alaska Anchorage Library.On September 29, 1940, Cooper committed suicide by hanging himself in the closet of a hotel room in the Park Central Hotel in New York City.