Karl Hopf was tried in Frankfurt am Main in January 1914 for poisoning members of his own family over many years. The prosecution charged him with four murders and three attempted murders. The jury convicted him of one murder, that of his first wife, Josefa, who died in 1902, and of four attempted murders: two later wives and two of his children. It acquitted him on the counts that concerned his father and his mother. He was sentenced to death and executed by guillotine at the Preungesheim prison on March 23, 1914.
The case became known well beyond Frankfurt for two reasons. Hopf, who had trained as a druggist, had bought live cultures of typhoid and cholera bacteria by mail, posing as the head of a laboratory, and used them against his third wife in 1912. And the Frankfurt court chemist Georg Popp found arsenic in the exhumed remains of Hopf's relatives and, in what the city of Frankfurt later described as a first, in the cremated ashes of his mother. A 2025 study in the American Journal of Forensic Medicine and Pathology calls the case the first thoroughly documented European instance of murder by deliberately administered bacteria.
Hopf was born in 1863 in Frankfurt into a well-off merchant family. According to the historian Gerhard Raiss, writing in the Main-Taunus district yearbook in 1994, he left the Musterschule early and trained as a druggist in London. The Wiener Zeitung, in a 2014 feature by Ulrich Zander, says he left the Gymnasium early and gained experience in the drug and chemical trade in London, Belgium, Morocco and India.
Damiani and Comacchio, the authors of the 2025 study, give a more exact sequence: military service in 1884, work in London drugstores in 1888, a move to Casablanca in 1889, and a return to Frankfurt in 1891 to recover from malaria caught in Morocco. He then worked in Brussels and London, where he first appeared on a variety stage. Raiss writes that he trained in foil and sabre fencing in England and Morocco and became very skilled; both Raiss and the Wiener Zeitung report that he won, or claimed, a world championship in sabre fencing in London, the Wiener Zeitung giving the year as 1891.
By the mid-1890s Hopf was back in Germany. Damiani and Comacchio date his return to 1894 and describe him as a breeder of Saint Bernards. Raiss places his settling in Niederhöchstadt, then a small village in the Taunus and now part of Eschborn, at about 1900. There he bred dogs with success. He wrote a book called Der St. Bernhardshund, worked on a remedy for canine distemper, and, according to both Raiss and the Wiener Zeitung, once sold a dog for 10,000 gold marks, a very large sum at the time.
The first two deaths later charged against Hopf came in the 1890s. His father, Wilhelm Hopf, died in 1895 after stomach and bowel symptoms that no one explained, Damiani and Comacchio write; there was some suspicion at the time, but it was directed elsewhere. The Wiener Zeitung reports that the father had lent his son 14,000 marks.
In 1896 a son was born to Hopf outside marriage. The child, Karl Richter, is named in the 2025 study; the Wiener Zeitung calls him "Karlchen" and says he was the child of an affair with a housekeeper and died at nearly one year old. Hopf was later charged with murdering both his father and this child. The jury did not convict him of murder in either case.
In the spring of 1902 Hopf married Josefa Henel at Niederhöchstadt. Raiss gives the date of her death as November 28, 1902, after a short illness, the same year as the wedding. Hopf collected 20,000 gold marks from a policy on her life, according to Raiss and the Wiener Zeitung. The Wiener Zeitung adds that a police report at the time claimed he had killed her with bacteria, an idea investigators then dismissed as absurd.
Josefa Hopf is the one person whose death the jury in 1914 held to be murder. Years later Hopf offered the court an explanation for the arsenic found in her remains: she had taken arsenic pills, he said, to improve her looks. The city of Frankfurt's 2011 profile of Georg Popp and the 2025 study both report this defense, which the jury rejected.
Hopf married again soon afterward. His second wife, Auguste Christine Schneider, was 20 years younger than he was, Raiss writes; the Wiener Zeitung gives her nickname as "Didi." She fell ill repeatedly while living with him in Niederhöchstadt. Her parents nursed her back to health, and each time she returned to her husband the illness came back. She divorced him, left, and remarried. She died not long after, officially of tuberculosis according to the Wiener Zeitung. A 30,000-mark policy on her life did not go to Hopf: Raiss says he could not collect it, and the Wiener Zeitung says it was paid to her new husband.
The couple's daughter, Elsa, died in Niederhöchstadt in 1906, Raiss writes. The Wiener Zeitung says she died five weeks after her birth.
The deaths around Hopf did not go unnoticed. Damiani and Comacchio report that formal suspicions about his first wife and his illegitimate son led to proceedings by 1907, which were dropped for lack of evidence, and that reports about his second wife and his daughter were also set aside.
Raiss describes how the local press handled the rumors. Neighbors in the Vordertaunus suspected Hopf of poisoning his wives and his daughter, and several papers, among them the Taunusbote and the Höchster Kreisblatt, printed those suspicions. Hopf answered with civil lawsuits, which silenced the reports. The editor of the Wiesbadener Tageblatt, which had also carried them, was fined 200 marks. The Wiener Zeitung likewise says he successfully sued his accusers, including several newspapers.
In 1908, Raiss writes, Hopf sold his property on Katharinenstraße in Niederhöchstadt, gave up breeding and moved to Frankfurt. He turned to the variety stage as a fencing performer. Under the name "Athos," after one of the Three Musketeers, he cut fruit tossed into the air; as "Captain Charles Vernon," according to Raiss and the Wiener Zeitung, he split an apple resting on the neck of a female assistant at the Schumann Theater. At his execution in 1914 the Flörsheimer Zeitung still described him as an artist and fencing instructor.
Hopf's mother, Auguste, was charged in the indictment as the victim of attempted murder, not murder, according to the 2025 study, which says she was 76 when she was poisoned. Her death date is not given in any source opened. The Wiener Zeitung reports that she left her son 27,000 marks. Her body was cremated, a fact that later made her remains central to the forensic argument at the trial.
In 1912, while on tour, Hopf married for a third time in London. His bride, Wally Siewec, had been born in Dresden; the Wiener Zeitung describes her as an Austrian from Dresden, and the indictment, according to Damiani and Comacchio, spelled her name "Siew." Hopf insured her life for 80,000 gold marks with a different company from before, under a mutual policy on both spouses (Raiss). The Wiener Zeitung says he led her to believe the policy was in her name only, and that she found papers showing her own life was insured too.
She soon became seriously ill with severe stomach and bowel symptoms and a dangerously high fever. Raiss describes Hopf as outwardly devoted, constantly at her bedside and constantly giving her medicine. The trial evidence, as Raiss summarizes it, was that he had swapped the opium tincture doctors had prescribed for her diarrhea for tincture of digitalis.
Hopf also used bacteria. Max Neisser, the bacteriologist appointed by the court, reported that a typhoid culture reached Hopf on July 19, 1912. Hopf's diary for July 31 carried the letters "W" and "B. Ta.," and Karl Lempp, writing in a criminology journal in 1921, concluded that on that day he began infecting his wife by mixing the culture into ground meat, when she was already weakened by arsenic and digitalis. Hopf recorded her temperature from August 5; her fever rose from August 7 and stayed high for weeks. Damiani and Comacchio compare his notes to the record of a clinical trial. He later admitted that he had also given her cholera bacilli. She did not fall ill from those, because the culture was no longer virulent.
Her parents finally had her admitted to the Diakonissenkrankenhaus in Frankfurt, according to Raiss. The Wiener Zeitung says she had resisted Hopf's treatment before she was admitted. In hospital she recovered. Hopf visited daily with flowers and gifts. Raiss and the Wiener Zeitung both report the finding that he had sprayed or coated the flowers with bacteria.
Hopf's bacterial cultures came by post. Damiani and Comacchio identify the supplier as the Král collection of microorganisms, a private collection founded in Prague in 1890 by František Král, acquired after Král's death in 1911 by Ernst Pribram and moved to Vienna in 1914. Earlier German accounts, including Raiss and the Wiener Zeitung, describe it simply as a bacteriological institute in Vienna. Hopf received 15 shipments. He ordered them on a forged letterhead for an invented "Chemical, Bacteriological and Therapeutic Institute Hopf." A Berlin bacteriologist, Max Piorkowski, had earlier refused his request for cholera, typhoid and streptococcus cultures. Hopf told the Vienna supplier, the Wiener Zeitung reports, that he needed the material to make medicine for dogs.
When the cultures disappointed him, Hopf wrote to complain that they had a very poor effect on humans, and asked for replacements. He had meant to write that they worked poorly on mice and guinea pigs. Raiss writes that the institute's staff read the word as "Meerschwein," guinea pig, rather than "Mensch," human, and took no action. In November 1912 he obtained cholera cultures again; the 2025 study suggests the material may have been linked to the Balkan Wars then being fought, and the Wiener Zeitung reports that he sought material from those battlefields.
The illness of Wally Hopf was what finally brought the police. At the Diakonissenkrankenhaus, according to Raiss, a doctor named Rossmann, a recognized specialist in toxicology, saw that she showed the signs of serious poisoning. He went to the detective responsible, von Salamon, who persuaded the examining magistrate, with some difficulty, to issue an arrest warrant. Von Salamon remembered an earlier newspaper report about a man of similar name in the Taunus whose neighbors suspected him of poisoning his family. The city of Frankfurt's 2011 profile of Georg Popp gives the same outline: the treating physician suspected that Hopf had tried to poison her and alerted the police.
Hopf was arrested on April 14, 1913. The city's 2011 account says he was taken after visiting his wife at the hospital; Raiss says he was arrested at the hospital; the Wiener Zeitung says on his way there. All three agree that he was prepared for the moment. Raiss writes that he had a vial of potassium cyanide in his waistcoat pocket and later said he had meant to drink it if he were caught, but the officers were too quick. The Wiener Zeitung says four officers prevented the attempt.
The same day, Georg Popp was called to the apartment to search it alongside the criminal police. Popp, born in Frankfurt in 1861, had set up as a public chemist in the city in 1889, had turned to forensic chemistry around the turn of the century, and was known for early work with fingerprints and soil traces. What he and the detectives found, the city's 2011 profile says, was a complete laboratory of poisons and deadly bacterial cultures. The Frankfurter General-Anzeiger called it "the Hopf Pandora's box" and wrote that it could have wiped out all of Frankfurt.
The 2025 study lists what the searchers recorded: arsenic, strychnine, bitter almond water, extract of deadly nightshade, foxglove, mercuric chloride, morphine, opium and cyanide; living cultures of cholera, typhoid and tetanus bacteria; and a culture of glanders that was no longer alive. Tests on animals found the tetanus culture extremely virulent, the typhoid culture highly virulent and the cholera culture weak. The apartment also held a library of medical and bacteriological works, pharmaceutical catalogs and two editions of the Criminal Code. Neisser later judged Hopf's knowledge from books on these subjects to be considerable.
Raiss and the Wiener Zeitung also report that the search turned up items and photographs from Hopf's private sexual life, and that the Frankfurt dog fanciers' club expelled him in part because of them.
Under questioning Hopf said he needed the poisons and the bacteria for experiments and to make medicines for his dogs, Raiss writes.
The arrest reopened every earlier death. The bodies of Hopf's father, his first wife and his children were exhumed, according to the Wiener Zeitung, and Raiss writes that Hopf was made to attend at the graves. Popp examined the remains in his laboratory and found arsenic.
His mother's case was harder, because she had been cremated. Popp and a colleague, Dr. Sieber, analyzed her bone ash, the 2025 study reports, and found arsenic there as well: 0.066 milligrams per 100 grams. To answer the objection that the arsenic might have come from the cremation itself, they ran experiments with dogs. They concluded that cremation adds no arsenic, that bone ash keeps about 15 to 17 percent of the arsenic present in the fresh bone, and that the level in the mother's ash pointed to a fatal dose before death. The city's 2011 profile describes this as the first time arsenic was detected and measured in the ashes of a cremated person. The criminologist Albert Hellwig published a study of the finding in 1915.
The sources do not agree on every result. Damiani and Comacchio write that arsenic was found in the exhumed bones of the first and the second wives. The Wiener Zeitung says that high arsenic levels were found in all the exhumed remains except those of the mother and the second wife.
Hopf's explanations, as reported in 2011 and 2025, were that his father had drunk too much Offenbach mineral water, that his first wife had taken arsenic as a beauty treatment, that he had advised his mother to take it for her metabolism, and that he had put arsenic on the bodies of his children after their deaths to slow decay.
For the attempt on Wally Hopf, the court relied on bacteriology as well as chemistry. Neisser used the Widal test, a blood test for typhoid devised in 1896, to compare her serum with the typhoid strain found in Hopf's possession. Her serum clumped that strain at a dilution of 1 to 3,200, the 2025 study reports, while other typhoid strains reacted only at much weaker dilutions. Damiani and Comacchio describe this as the first documented forensic use of the test, linking a specific culture in the accused's hands to the illness of the victim. Neisser published an account of the bacteria in the Hopf case in the magazine Die Woche in 1914.
Raiss writes that Hopf confessed at the cemetery during an exhumation, confronted with the open grave and the weight of the evidence. The criminologist Erich Wulffen, as summarized by Damiani and Comacchio, recorded that Hopf admitted he had married his third wife only in order to kill her and collect the insurance, as with his earlier wives, and that he later tried to soften this by saying the idea had come to him only after the wedding. The Wiener Zeitung says he admitted mixing arsenic and bacteria in his poisonings, admitted sending Wally the flowers, and, during the trial, confessed to killing Josefa.
The trial before the Frankfurt jury court opened on January 12, 1914, according to the 2025 study. Raiss describes a packed courtroom and crowds outside the court building that brought traffic to a halt; parked carriages were rented out as viewing stands, and eight photographers and several newsreel cameramen waited for a picture of the defendant. Sixty-four witnesses and experts were called, Raiss writes; the Wiener Zeitung says more than 60. The Prager Tagblatt in Prague carried a report on January 16 headed, in translation, the poison murderer Hopf in court, according to the 2025 study.
The indictment, as Damiani and Comacchio list it, charged completed murder in four cases, those of Josefa Hopf, Elsa Hopf, Karl Richter and Wilhelm Hopf, and attempted murder in three, those of Christine Schneider, Wally Hopf and Auguste Hopf.
Much of the hearing turned on science. Popp had to explain and defend his new methods again and again, even to other experts, so that at times the trial resembled a forensic seminar, the city's 2011 profile says. The prosecutor, as Raiss quotes him, called Hopf's method a new kind of murder that had to be called scientific murder. The Wiener Zeitung reports a similar phrase, a "new method of murder."
After six days of hearings, Raiss writes, the jurors withdrew and returned after one hour and 20 minutes with a unanimous verdict. The Flörsheimer Zeitung, a local paper in Flörsheim am Main, reported the result in detail in March 1914. On January 17 the jury found Hopf guilty of poisoning his first wife; of attempting to poison his second and his third wife; and of attempting to poison his illegitimate child and his legitimate child. It found him not guilty of the attempted poisonings of his father and his mother with which he had been charged. The court sentenced him to death for the murder and to 15 years of penal servitude for the four attempts, with the usual additional penalties. Damiani and Comacchio give the same outcome: one murder, attempted murder of both later wives and both children, acquittal on the father and the mother, death for murder and 15 years for the attempts.
The verdict meant that, in law, Hopf was a murderer once. The deaths of his infant son and his daughter, which had been charged as murders, ended as convictions for attempted murder, and the death of his father, also charged as murder, ended in acquittal.
Not every later account reports the verdict this way. Raiss, in 1994, wrote that Hopf was convicted of poisoning his father, his first wife, an illegitimate infant and his daughter, and of three attempted poisonings, of his mother and his second and third wives. That list matches the charges rather than the verdict reported in 1914. The Wiener Zeitung's 2014 account says he was convicted of Josefa's murder and gives the trial and verdict dates as January 20 and February 17, 1914, dates that the contemporary reports do not support.
The trial was read in its own time as a study in the psychology of poisoners. The physician Albert Eulenburg, a Privy Medical Councillor, wrote a commentary after the trial, reprinted in May 1914 in a German-language paper in Grand Island, Nebraska. He described Hopf as a druggist and fencing instructor accused of six poison murders, noted that most of his victims had been women, and recalled that the poisons had included pure bacterial cultures from a Vienna laboratory. Eulenburg used the case to question the common belief that poisoning was mainly a crime of women.
Hopf did not escape the sentence. On the Sunday evening before the execution, the prosecutor told him that the King had not used his power of pardon and that the execution would take place the next morning, the Flörsheimer Zeitung reported. The Wiener Zeitung says he had declined to seek clemency. He stayed calm, as he had been throughout the trial. He asked for bread, sausage and several bottles of beer, smoked, and wrote a letter to his last wife. The prison chaplain could not bring him to express remorse. He slept soundly, woke at four, smoked again, ate breakfast and asked for more coffee.
At 7 a.m. on Monday, March 23, 1914, he was executed in the courtyard of the prison at Preungesheim, in Frankfurt, by the executioner from Magdeburg. The Institut für Stadtgeschichte, Frankfurt's city archive, records the execution at that hour in its chronicle of the city for 1914. The Flörsheimer Zeitung wrote that he walked to the scaffold with his head held high and showed no sign of remorse. Raiss gives the time of death as 7:04 a.m. and writes that, as no relative claimed the body, it went to the University of Marburg for the teaching of medical students.
The case raised a question that German law had barely addressed: who could buy dangerous bacteria. In the Reichstag, the National Liberal deputy Keinath called for a ban on the trade in poisonous bacterial cultures, and the Social Democrat Dr. Quarck called for national and international rules, according to Damiani and Comacchio. The criminologist Paul Näcke assured the public that German institutes had denied Hopf virulent strains, a claim the 2025 authors call only partly true, since he obtained 15 shipments elsewhere. Before 1917, they write, the rules in Germany and in Austria were aimed at accidental infection; sellers did not have to check a buyer's credentials. On November 21, 1917, new regulations of the Federal Council required proof that a buyer was authorized.
In the fourth of his introductory lectures on psychoanalysis, given in 1915 to 1917, Sigmund Freud discussed a man he called only "H.," who had been charged with murder. H. had obtained cultures of dangerous germs from scientific institutes by posing as a bacteriologist and had used them against close relatives. In a letter complaining that a culture had not worked, he wrote of his experiments on people when he meant his experiments on mice and guinea pigs. The doctors at the institute noticed the slip but drew no conclusion. Freud asked whether they should have treated it as a confession. He concluded that it would have struck him as suspicious but would not by itself have justified an investigation. Damiani and Comacchio identify H. as Hopf, and they report that the misworded letter came up at the trial as evidence. Freud's student Theodor Reik later used the same slip in his own work.
In Frankfurt the case is remembered mainly through Georg Popp. The city's 2011 profile, written by the author and journalist Sabine Hock for the 150th anniversary of Popp's birth, opens with the judgment that without the court chemist the poisoner would probably never have been caught. Popp received a teaching post at the new University of Frankfurt's institute of forensic medicine in 1919, became an honorary professor of forensic chemistry and criminology in 1924, and died in 1943. The novelist Nikola Hahn built her historical crime novel Die Farbe von Kristall around his cases, Hopf's among them, the profile says.
The former judge Thomas Schnepf published a book on the case, Frankfurter Giftmorde: Der Fall Karl Hopf, in 2021. In 2025 Damiani and Comacchio placed the case at the start of the history of biocrime, the use of living pathogens to kill for private motives, as distinct from bioterrorism.
How many people he killed. Hopf was convicted of one murder. The jury acquitted him on his father and mother and convicted him only of attempts in the cases of his two children and his second and third wives. Contemporary commentary, such as Eulenburg's reference to six poison murders, and some later accounts, including Raiss's 1994 article and Popp's 2011 profile, describe him as having killed his parents, wives and children. Those are allegations or the charges, not the verdict.
The second wife. Christine Schneider died after leaving Hopf and remarrying, officially of tuberculosis. Her death was not charged as murder; the conviction concerned an attempt to poison her while she lived with him. The sources disagree on whether arsenic was found in her remains.
Trial and verdict dates. The 2025 study says the trial opened on January 12, 1914; Raiss says January 19, which cannot be right if, as he and the Flörsheimer Zeitung both say, the verdict came on January 17. The Wiener Zeitung's dates of January 20 and February 17 are not supported by the contemporary report.
The supplier of the cultures. German accounts speak of a Vienna institute; the 2025 study identifies a Prague collection that moved to Vienna only in 1914.
Firsts. Popp's 2011 profile calls the trial probably the first in the world in which a forensic chemist's analyses led to a poisoner's conviction on circumstantial evidence, and Raiss calls it the first such trial worldwide. The detection of arsenic in exhumed bodies was not new in 1913; what the city profile claims as new is the detection and measurement of arsenic in cremated ashes. The 2025 study's claim that this was the first forensic use of the Widal test is the authors' own assessment.
Conan Doyle. Damiani and Comacchio note that British newspapers reported Hopf's arrest and his bacterial cultures in April 1913, and The Lancet in May 1913, months before Arthur Conan Doyle published "The Adventure of the Dying Detective," in which a villain kills with cultured germs. They see parallels, but Doyle never named Hopf as a source, and the authors present the link as an interpretation.
1863: Karl Hopf born in Frankfurt am Main.
1884: Military service.
1888: Works in London drugstores.
1889: Moves to Casablanca.
1891: Returns to Frankfurt with malaria.
1894: Back in Germany; breeds Saint Bernards.
1895: Father, Wilhelm Hopf, dies after unexplained stomach symptoms.
1896: Illegitimate son, Karl Richter, born; he dies in infancy.
Spring 1902: Marries Josefa Henel at Niederhöchstadt.
November 28, 1902: Josefa Hopf dies; Hopf collects 20,000 gold marks.
After 1902: Marries Auguste Christine Schneider, who falls ill repeatedly, divorces him and later dies.
1906: Daughter Elsa dies at Niederhöchstadt.
By 1907: Proceedings over the first wife and the son are dropped for lack of evidence.
1908: Sells his Niederhöchstadt property and moves to Frankfurt; performs as "Athos."
1912: Marries Wally Siewec in London; insures her life for 80,000 gold marks.
July 19, 1912: A typhoid culture reaches him.
July 31, 1912: Begins giving his wife typhoid bacteria, according to the court bacteriologist and Lempp.
November 1912: Obtains cholera cultures again.
April 14, 1913: Arrested in Frankfurt; Georg Popp and the police search his apartment.
1913: Exhumations; Popp finds arsenic in the remains, and in the mother's cremated ashes.
January 12, 1914: Trial opens before the Frankfurt jury court.
January 17, 1914: Convicted of one murder and four attempted murders; acquitted on his father and mother; sentenced to death and 15 years of penal servitude.
Sunday evening before the execution: Told that no pardon will be granted.
March 23, 1914: Executed by guillotine at 7 a.m. in the Preungesheim prison yard.
November 21, 1917: New Federal Council rules require proof of authorization to buy bacterial cultures.