While many historical whodunnits were solved not long after the supposed crime was committed, sometimes it's up to modern science and history to determine how and why a person died. Here are cases where murders were revealed or refuted decades or even centuries after the fact.

Top image shows the death of Giuliano de' Medici.

1) The Blood Transfusion Murder

The Decedent: Antoine Mauroy, a Parisian madman who died after receiving multiple transfusions of calf's blood in the winter of 1667.

The Mystery: Who or what was really responsible for Mauroy's death?

When blood transfusions first appeared on the medical scene, they were met with a great deal of controversy. Dr. Jean-Baptiste Denys, the personal physician to King Louis XIV, performed the first xenotransfusion in June 1667, transfusing blood from a sheep to a 15-year-old boy. The boy survived, and Denys later tried a similar procedure on Antoine Mauroy, hoping the infusion of animal blood might treat Mauroy's insanity. Mauroy died within a few weeks of the procedure, and Denys was tried for murder.

Denys was acquitted, and eventually suspicion fell on Perrine Mauroy, Antoine Mauroy's abused widow. Perrine was convicted of poisoning her husband with draughts of arsenic, but the judge suspected that she had help. And in her book Blood Work: A Tale of Medicine and Murder in the Scientific Revolution, historian Holly Tucker uncovered evidence that Perrine did, in fact, have help in the murder of her husband — help from Denys' scientific rivals, who hoped to discredit his work. And Mauroy's death did, in fact, put an end to Denys' blood experiments. He retired from medicine and blood transfusions were banned in France in 1670.

2) The Murdered Warlord

The Decedent: Cangrande della Scala, ruler of Verona who took control of other Italian cities during the 14th century. He died suddenly in 1329 at the age of 38.

The Mystery: Did Cangrande die of natural causes? Or was he murdered?

After Guecello Tempesta, ruler of Treviso, surrendered his city to Cangrande, Cangrande fell deathly ill. The official account at the time was that Cangrande became ill because he had drunk from a polluted stream. However, there were rumors that he had, in fact, been murdered.

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Recently, Cangrande's body was exhumed to determine whether those rumors could be true. An autopsy, which included testing fecal matter, found that Cangrande had consumed deadly digitalis, also known as foxglove. The researchers found that the amount of digitalis found was consistent with a deliberate poisoning.

We don't know who would have been responsible for this poisoning, but one suspect is Mastino II, Cangrande's nephew and successor, who had Cangrande's physician hanged following Cangrande's death.

3) Malaria, Not Murder Did in These Medicis

The Decedents: Francesco I de' Medici and his second wife, Bianca Cappello, who died within a day of each other in 1587.

The Mystery: Did their near-simultaneous deaths mean they were murdered?

When a husband and wife die within a day of each other, it can seem a bit suspicious, and even though the deaths of Francesco I de' Medici and wife were initially attributed to malaria, it didn't take long for people to cry murder. The suspected murderer (or power behind the murder) was Francesco's own brother, Cardinal Ferdinando.

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While Francesco's remains do contain high levels of arsenic, forensic anthropologist Gino Fornaciari said that's consistent with embalming practices at the time. Fornaciari found P. falciparum proteins in fragments of Francesco's bones, which point to a death by malaria. Such proteins were not found in the bones of Francesco's father or his first wife. In Fornaciari's forensic opinion, Cardinal Ferdinando should be cleared of his brother's murder.

[Discovery News]

4) A New Assassin's Creed Character?

The Decedent: Giuliano de' Medici, who was set upon by a gang of men with knives in the Duomo cathedral in Florence in 1478. His brother Lorenzo escaped the assassination attempt.

The Mystery: Who, besides Francesco de Pazzi, orchestrated the coup?

There's a reason it's called the Pazzi conspiracy; the stabbing of the two Medici brothers has long been linked to Francesco de Pazzi, member of a rival family. But one of the chief minds behind the plot wasn't connected to it for centuries. In 2004, historian Marcello Simonetta announced that he had decyphered an encrypted letter that revealed that Federico da Montefeltro, duke of Urbino, was a major player in the plot. In the letter, the duke insists on getting rid of the brothers and reveals that he provided his own military forces for the plot.

[New York Times]

5) The Skeletons in the Well

The Decedents: 17 people whose bodies were discovered in a Medieval well in Norwich, England.

The Mystery: Why were these bodies in a well instead of properly buried?

In 2004, the remains of 17 people were discovered while a site was being excavated in Norwich for a future shopping center, and it presented Professor Sue Black, a forensic anthropologist at the University of Dundee's Centre for Anthropology and Human Identification (and star of BBC Two's History Cold Case), with a mystery: why were these people so disrespectfully disposed of?

At first, the archeologists who led the excavation suspected these were the bodies of plague victims, but carbon dating placed the decedents in the 12th or 13th century, before the plague hit England. DNA expert Dr Ian Barnes was brought in, and he found a DNA sequence in five of the skeletons that traced them to a single Jewish family.

Although it's not clear exactly what happened to these people, the researchers who worked on the case suspect that their deaths were linked to religious persecution. Natural deaths were ruled out, and the likely cause of death was either a mass execution or a group suicide. The bones were later buried in a Jewish cemetery.

[BBC News]

6) The Secret Assassination of an American President? Not So Fast.

The Decedent: Zachary Taylor, 12th President of the United States, who suddenly fell ill and died in 1850.

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The Mystery: Did Zachary Taylor die of a stomach ailment? Or was he murdered by anti-abolitionists?

On July 4th, 1850, President Taylor began to have stomach cramps and five days later he was dead. At the time, his doctors attributed his death to a stomach ailment, but historian Clara Rising, while working on a novel about Taylor, noted that his symptoms were consistent with arsenic poisoning. She speculated that anti-abolitionists, discontent with Taylor's opposition to slavery in the Western part of the country, had poisoned the president. Forensic anthropologist William Maples agreed it was a possibility, and Taylor's body was exhumed.

But anyone hoping to uncover a century-and-a-half-old murder was disappointed. Forensic pathologist George Nichols did detect arsenic in Taylor's remains, but not enough to indicate a poisoning. Rather, he ruled that Taylor's death was largely due to a natural ailment that led to gastroenteritis. That hasn't closed the book on Taylor's death for some, however; you'll still hear claims that the president was murdered.

[LA Times]

7) The Boy in the Cellar

The Decedent: An unknown boy, 15-16 years old, discovered in a 17th-century cellar in Maryland.

The Mystery: Who was this boy and why was he buried there?

When you find a body buried in a clandestine grave in someone's home, it's fishy right off the bat. The boy found by Erin Cullen as part of the Lost Towns project was probably buried between 1665 and 1675 in order to cover up the manner of his death. Forensic anthropologist Douglas Owsley examined the body and found a fractured wrist that likely came before a violent death. Owsley's team surmised that the boy was likely an indentured servant who was abused, killed, and then awkwardly buried so no one would learn how he died. Around that time, laws were passed in the area forbidding private burial for this very reason, but this boy was an unfortunate victim of violence and was hidden away for centuries.

[Smithsonian]

8) CSI: Napoleon

The Decedent: Napoléon Bonaparte, two-time Emperor of France who died in exile in 1821.

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The Mystery: Did Napoleon die of natural causes, or was he poisoned by his captors?

While Napeleon's physician ruled that the cause of the former emperor's death on Saint Helena was a stomach ulcer, there has been some suspicion that he was poisoned, perhaps by his British captors. In a 1961 paper in Nature, physician and amateur toxicologist Sten Forshufvud proposed that Napoleon's symptoms were consistent with arsenic poisoning, fueling further speculation that the people charged with his care were to blame for his death.

High levels of arsenic have been found in Napoleon's hair, but that's not unusual for the period. Many cosmetics, including hair tonic, contained arsenic. And there is no evidence of hemorrhaging of his heart or other indicators of arsenic poisoning. Pathologists who have examine Napoleon's stomach, however, see little doubt of the cause: the body shows clear signs of stomach cancer and a grainy substance found in the stomach indicates gastrointestinal bleeding, which most likely did Napoleon in.

[National Geographic]

9) The Mercurial Mystery of Tycho Brahe

The Decedent: Tycho Brahe, 16th-century nobleman, astronomer, alchemist, duelist and all-around colorful dude.

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The Mystery: There has long been a theory that Brahe, who seemed to die of a bladder infection in 1601, was actually murdered. The supposed culprits? Possibly the Danish King Christian IV, who wasn't a fan, or perhaps Brahe's own assistant Johannes Kepler. The supposed method? Mercury poisoning.

We don't know for sure what did in Brahe, but it probably wasn't mercury that did it. The most recent exhumation of Brahe's body allowed researchers to find that, while there were trace amounts of mercury in Brahe's beard, there wasn't nearly enough to indicate murder. They didn't find evidence of any other poisons, either. So Kepler's off the hook... for now.