You can deduce a lot about a madman by the way he is perceived by others. The conventional anecdotes are the staple of many retellings of their crimes. They were loners. They didn’t talk to anyone. Some thought of them as socially awkward. They never stood out, always seeming to disappear among the faces in crowds. And then there are the sorts whose sins come as a total surprise to onlookers who otherwise thought highly of the culprits. “No one expected a sweet man like him to murder those boys,” a resident in Houston, Texas once said of Dean Corll. “I considered him a friend, and I’m stunned by this all,” another spoke of John Wayne Gacy, shortly after his house was ransacked and 29 bodies were pulled from the crawlspace beneath. The more lurid and disturbing maniacs cast a long shadow of doubt amongst their peers, who would never assume something so heinous behind a set of charismatic eyes. That also means their crime sprees tend to be long and drawn out, no doubt since they provide few (if any) warnings signs. Yet as I watched “Tenderness of the Wolves,” a dramatic reenactment of the many crimes of Fritz Haarmann, I was struck by the almost cheerful ambivalence of his friends, lovers and onlookers as he routinely got away with the vicious killings of teenage runaways. Consider a scene, for example, when the notorious “Werewolf of Hannover” drops a slab of meat on the counter of a lady’s establishment, and she expresses glee at his arrival. He apparently doubles as a butcher, in addition to being a police informant. Others, however, find the texture of his delivery odd and off-putting (no one questions where it comes from, of course). But the restraint of curiosity belongs to a single pitch: what purpose is there to suspect a man so charismatic of engaging in anything so heinous? This is a movie that theorizes people are more content to look the other way on what is obvious than to deal with it directly.