Four French doctors who examined the body of a 10-year-old boy in the Prison du Temple on June 9th, 1795, concluded the child died of bone tuberculosis.
One of them, Philippe-Jean Pelletan, surreptitiously removed the dead boy's heart, coated it with flour, wrapped it in a handkerchief and hid it in his pocket. The body was thrown into a mass grave, but as a result of Dr Pelletan's act, Prince Louis de Bourbon, Duke of Anjou and successor to the kings of France, was able to announce on April 19th that "more than two centuries of mystery have ended today".
Based on DNA testing, scientists concluded that the heart kept since 1975 in a reliquary in the royal crypt of St Denis Basilica was indeed that of Louis XVII, son of Louis XVI and Marie-Antoinette. The king and queen were guillotined two years before their son died. More often used to identify rapists, murderers or reluctant fathers, DNA testing has also become the ultimate tool of the historian.
Like the Russian Grand Duchess Anastasia, Louis XVII inspired a legion of crooks and madmen in the 19th century, all claiming they had escaped from the revolutionary prison and were the authentic royal heir.
One of them, a Prussian watchmaker named Carl Wilhelm Naundorff, was buried in a tomb marked, "Here lies Louis XVII, Duke of Normandy, King of France and Navarre". Between 1993 and 1998 a team of scientists compared genetic material from Naundorff's arm with DNA from the hair of Marie-Antoinette and her two sisters. The verdict was categorical. Naundorff was a fraud.
Attention then turned to the heart at St Denis, which the 18th century Dr Pelletan had preserved in a crystal vase filled with alcohol. The restoration Bourbons refused to take it from Dr Pelletan in 1828, so he consigned the heart to the Archbishop of Paris. But in July 1830 the archbishop's palace was sacked in another revolution. The crystal vase was smashed, and Dr Pelletan's son,, Philippe-Gabriel, found the royal heart amid crystal shards, covered with sand.
Last December, at the request of the historian Philippe Delorme and with the consent of the Bourbon descendants, another group of French doctors opened the reliquary in the St Denis crypt to examine what they described as "a human heart of small size, corresponding to that of a child between five and 10 years of age".
The heart tissue was "dried up, contracted and of a petrified consistency", they reported. Although its DNA was "very degraded", it took only four months for the chains of nucleotides to prove that the boy who died in the prison was Louis XVII.
The Bourbon family has requested permission to bury his heart alongside his father and mother.
By coincidence, on the same day that Louis XVII's heart was identified, lawyers for the family of four-year-old Gregory Villemin requested DNA testing in the hope of solving his October 1984 murder. "Little Gregory", as the whole country came to know him, was drowned in the Vologne river in eastern France with his hands and feet bound.
His case became the judiciary saga of the 1980s. The first cousin of Gregory's father - and his mother's lover - was at first suspected of having murdered the boy. The cousin was freed after three months in prison, but was shot dead by Gregory's father, who persisted in believing him guilty. Then Gregory's mother, Christine, was charged with killing her own child, only to be acquitted in 1993.
It seemed France would never learn who killed little Gregory. Then lawyers had the idea of testing DNA from the saliva on the back of a stamp used to post an anonymous threatening letter before Gregory's death. If the Dijon court of criminal appeal agrees - and each DNA test costs more than £3,000 - the problem will be knowing whose DNA to compare it to, since there are no suspects left in the case.
The prosecutor is reluctant to exhume the body of the cousin murdered by Gregory's father because he could not be charged or tried even if the DNA matched.
DNA testing has often cleared those falsely accused. The actor Yves Montand refused to provide a DNA sample in a paternity suit filed against him by Aurore Drossard, the daughter of a former mistress. Based on Ms Drossard's strong physical resemblance to Montand and witnesses' testimony, a court ruled that she was his daughter.
But six years after Montand's death - and the controversial exhumation of his body - a DNA test proved the court wrong. Human judgment, it seems, cannot compete with the test-tube. A recent US Department of Justice report advocated maximum use of DNA testing and concluded that the high number of convicted criminals cleared in this way "shakes belief in the justice of court verdicts".
