The real Mr Dupont de Ligonnès, from Nantes (Loire-Atlantique), has been a murder suspect and on the run from police ever since his wife, four children, and the family’s two dogs, were found buried in the garden of their family home, in 2011 - in a case that shocked France at the time.
On Friday October 11, police in Scotland stopped a man at Glasgow Airport after he disembarked a flight from Paris. He was arrested on a European Arrest Warrant originally issued by the French authorities, after an "anonymous tip-off" in France.
According to the Agence France-Presse (AFP), the man was first spotted at Roissy-Charles-de-Gaulle airport in Paris, but police there did not have time to arrest him before his flight took off, and instead alerted Interpol.
This led to his arrest in Glasgow.
Police information, and cooperation between French and Scottish police and Interpol, had suggested that the man was the wanted killer.
Police Scotland later said they were “certain” they were correct, after reportedly receiving "identification resources" from the French police.
French sources said that Scottish police were “affirmative” that this man was the killer, based on early fingerprint tests.
But later DNA tests eventually showed that the arrested man was not Mr Dupont de Ligonnès, and he was released - but not before news outlets around the world had reported the case.
Despite initially appearing sure that the man was the killer, French and Scottish police began to find inconsistencies in the case later in the night.
Early reports - including from trusted newswires Reuters and the AFP - had said that fingerprints taken from the arrested man had appeared to match those on file at Interpol belonging to Mr Dupont de Ligonnès, according to Scottish police.
This was later found to be incorrect.
Details on how suspects' fingerprints are checked have since emerged, with a view to shedding some light on how the error was made.
Fingerprinting expert Fabrice Mouton explained to FranceInfo that the vast majority of human fingerprints can be categorised as one of three official patterns: loops, whorls, and arches. This is the first stage of identification.
The second stage includes analysis of "minutiae" of the fingertips; the ridges on our fingers and palms. These can take considerably different forms depending on the person, with terms for their variations including "bifurcations" and "lakes".
Mr Mouton told FranceInfo: "In France, we consider that from the point at which 12 minutiae are visible and matched, we can track a print to formally identify someone."
The number of print minutiae required by law to formally identify a suspect can vary significantly between countries. This may have led to the errors made in this case, experts have suggested.
Early reports in this case said that just five minutiae were matching between the prints of Mr Dupont de Ligonnès and that of the arrested man - a much lower amount than required by French law to link a suspect.
Mr Mouton said: "The fewer number of minutiae...the more chances of the results matching with more people. Announcing a [definite] identification with only five minutiae in common appears rather hasty."
Similarly, police in Limay, Yvelines - where the arrested man had been living - later interviewed the man's neighbours, and found one who said he had known the accused for 30 years, and that he was definitely not Mr Dupont de Ligonnès.
Other neighbours agreed.
Further tests of evidence found in Yvelines did not match those on file for the killer.
Well after midnight, the Agence France-Presse tweeted that “some uncertainty” had emerged, especially after the fingerprints had turned out to be incorrectly linked.
By 12h56, the AFP confirmed: “The man arrested in Glasgow is not [Mr] Dupont de Ligonnès, after a negative DNA test (according to a source close to the case).”
The man has since been confirmed as a retiree from Yvelines, who splits his time between Yvelines and Scotland, and has no connections to the Mr Dupont de Ligonnès case.
L'homme arrêté à Glasgow n'est pas Dupont de Ligonnès, après un test ADN négatif, selon une source proche de l'enquête #AFP— Agence France-Presse (@afpfr) October 12, 2019
Audrey Goutard, police specialist and journalist at France Télévisions, told FranceInfo: “Us journalists moved at the same speed as the police, with the risks that that entails.”
She said that she had “called the highest police authorities, who confirmed 100% that this was Mr Dupont de Ligonnès. They based that on the words of their Scottish counterparts. The first DNA markers appeared to correspond. We had our sources, and we thought there was ‘no problem’.”
Investigations into how the error occurred are ongoing.
Some newspapers, including Le Monde, had stopped short of saying that the arrested man was definitely Mr Dupont de Ligonnès, instead writing that it was "yet to be confirmed".
Certains se demandent comment auraient dû réagir les médias dans l’affaire #XavierDupontdeLigonnes— Samuel Etienne (@SamuelEtienne) October 12, 2019
Voici une démonstration d’élémentaire prudence journalistique par @lemondefr pic.twitter.com/GMcpJuJ6cj
Police and journalists have been criticised for appearing to act without higher authority from those investigating the case directly, and said that police in Scotland should have waited for more confirmation from, and communication with, France before acting or making a statement.
Xavier Ronsin, president of the court of appeal in Rennes, and prosecutor in Nantes at the time of the Mr Dupont de Ligonnès case, wrote on Twitter that “only the prosecutor of the Republic in Nantes had the authority to communicate [this], and no other authority”.
Ça veut dire quoi "autorités" ? Facile sous couvert d'anonymat et de protection des sources d'affubler quiconque de ce titre. Seul le #procureur de la République de Nantes était habilité à communiquer et aucune autre autorité #justice #média #déontologieVariable #XDDL https://t.co/ovI5h7Huow— Xavier RONSIN (@xavierRonsin) October 12, 2019
Yet, France 3 police specialist Nathalie Perez told FranceInfo that she does not believe that police should have waited for “official communication” from France before acting.
She said: “Prosecutors often communicate through press conferences...I trust my sources of more than ten years; they are trustworthy people, who, this time, were sadly mistaken due to information coming from foreign authorities.”
Yet, Ms Perez admitted that in the event of future similar cases, it might be wise to wait for official confirmation from the original police investigators to corroborate initial police reports.
Since 2011, there have been more than 1,000 reported sightings of Mr Dupont de Ligonnès - across France, in Corsica, and Italy. But investigations have so far revealed nothing.
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