Normal (2009)

Dreaded serial killer Peter Kurten voluntarily turns himself over to the authorities. A young lawyer, eager to prove Kurten's mental derangement, agrees to defend a man who terrorized Germany between 1929 and 1931. In studying the case and meeting with the intelligent, cold-blooded manipulator, the young idealist's values become warped.

Unfortunately the movie Normal is not yet available on HBO Max.