When I first received Karl Berg’s book The Sadist, I opened it at once. It’s one of the earliest detailed clinical examinations of a brutal, blood-starved serial killer. Since Berg had also created a rudimentary profile from crimes he’d linked, as well as performed the victims’ autopsies, when he finally came face-to-face with the sadistic offender, Peter Kürten, his perspective was unique.

In this narrative, we first see Berg’s experience as the bodies turn up, stabbed, bludgeoned, or choked, which prepares us for the “monster.” When the police make an arrest, we know what’s next: Kürten speaks. He was among the worst of the worst, and as a clever, calculating psychopath he freely described to Berg what he’d done to each victim.

There’s a clear difference between the recorded facts of a case and the way a killer tells his or her own story. The raw quality of such confessions makes us feel as if we’re in the same room.

 It’s disturbing yet titillating, grotesque and wondrous. How, we ask, can a person get this way?

After Kürten’s conviction in 1930, Dr. Karl Berg went to his prison cell to study him – initiating one of the earliest attempts to thoroughly understand the abnormal mind of a repeat offender. He wanted the full story as Kürten would tell it, so he kept him under observation for a year.

Kürten confessed freely to Berg in shocking detail, which became the basis for Berg’s now-classic book, Der Sadist, later translated for the Library of Abnormal Psychological Types. Berg had already heard many of the details, but he got Kürten to reveal even more.

By this time, Berg was a part-time professor of forensic medicine at the Düsseldorf Medical Academy and the Medical Director of the Düsseldorf Institute of Legal and Social Medicine, which he had founded. In addition, he was a medico-legal officer of the Düsseldorf Criminal Court. This put him in prime position to evaluate Kürten, but Berg also recognized the opportunity he had to thoroughly study a rare type of criminal.

Not only was Kürten a psychopathic serial killer, he also had a peculiar paraphilia: he grew aroused from drinking his victims’ blood. Like most psychiatrists of his era, Berg was thoroughly acquainted with Richard von Krafft-Ebing’s work, so he knew how unlikely it was that he would see another such criminal during the course of his career. Thus, Berg sought to probe the soul of this strange and enigmatic man. He found his task, distasteful as it was, quite absorbing. 

He organized the material with the facts of Kürten’s crimes placed first, and the prison interviews second. He finished by analyzing Kürten’s character in light of what was then known about the paraphilic character disorder, sadism.

Although at trial Kürten had pled not guilty by reason of insanity, claiming he had a compulsive blood lust, he’d provided clear-headed details of his long life of crime. For those aspects of the crime in which Kürten had taken great pleasure, his memory was quite accurate. He began with the first and reeled them off in chronological order until he was finished.

Whenever his audience had looked horrified, he’d leered, clearly enjoying the effect he was having on them. For the court, Kürten reeled off crimes for which he had not even been accused, culminating in seventy-nine different criminal incidents (including thirteen murders).

Berg considered Kürten the most interesting personality in criminal history, due to his cleverness and diversity. What stood out was Kürten’s unusually accurate memory, which clearly facilitated his waking fantasies, and his sharp eye for minor details that alerted him to a vulnerable person. His first murder had been impulsive. The child was there, asleep. He’d tried to tear open her vagina, but it did not arouse him so he’d cut her throat instead. This had worked.

Kürten, Berg decided, was a psychopath whose sex impulse was perverted in an abnormal psychic constitution. He was born with a “predisposition for deviation” and his early experiences had conditioned him toward abnormality. With fantasies, he reinforced it.

In fact, after going through quite a number of evaluations, Kürten remembered an incident from his childhood. When he was nine years old, he was playing with other boys on an improvised raft. One boy fell off and Kürten pushed him under, drowning him. On another occasion, he pushed a boy off the raft to let the current carry him away. In both incidents, Kürten knew he’d done something wrong but felt pleasure rather than remorse.

Thereafter, he cultivated an inclination to lie. He learned how to pass as a normal person, but he kept the fire of his secret perversions alive. Berg estimated that his condition was 90% sadism, 10% atonement for injustice done to him.

Among the things Berg learned were that Kürten sometimes sought out pain, saying that he provoked the victims to strike him, indicating a masochistic component to his arousal. He visited his victims’ graves repeatedly, digging with his fingers into the dirt to renew his excitement; he also went back to where he had violated certain victims. He once witnessed a man fall under a train and he pretended to help just to get near the blood, which produced an orgasm.

Kürten enjoyed reading crime accounts in the newspapers and had read about Jack the Ripper several times. He considered nailing one body to a tree to produce public excitement. He preferred movies where a film promised the possibility of someone being strangled or stabbed.

Berg’s detailed study set a standard for the future. Going beyond mere case analysis, he offered a means for other professionals to consider the psychological details of sadism. This book can be difficult to acquire for an affordable price. I offer more from it, with other portraits, in The Mind of a Murderer.

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