German cinema of the 1930s -- straddling the Weimar Republic and the Third Reich -- is full of documentary-like sequences detailing the detective work of the criminal police. Two notable sequences are below. The first is from Fritz Lang's classic 1931 film, M. The second is from Erich Engels' 1938 ode to Nazi Germany's police detectives, Mordsache Holm (The Holm Murder Case).
M (dir. Fritz Lang, 1931)
This documentary-like sequence from Fritz Lang's 1931 film M explains state-of-the-art detective work in the late Weimar Republic. The sequence has moments of humor (note the fingerprint card for the gangster nicknamed "Vierfingerernst" (Four-finger Ernst) and the pedantic tone of the graphologist). It also has moments of admiration for careful detective work and moments of utter hopelessness that it will lead to an arrest. But what's with that giant overhead projection of a fingerprint?!
Mordsache Holm (dir. Erich Engels, 1938)
The police operate with care and precision in Erich Engels' film, as they investigate a crime scene and record the clues that will eventually lead them to the murderer. The documentary-like montage sequence probably owes a direct debt to Lang's sequence from M. l love the fact that it is literally a red thread found under the victim's fingernail that leads the police to the killer!