Where is King Henry IV’s head? Scientists thought they had figured it out, but now they’re not so sure.

French monarch Henry IV is probably best-known for issuing the Edict of Nantes, which granted civil rights to Protestants in a nation that was still mostly officially Catholic. While he enjoys a good reputation posthumously, at the time Henry faced distrust from both Protestants or Catholics. French Protestants resented Henry’s pragmatic decision to convert from his original Calvinist faith in order to ascend the throne, while Catholics were suspicious of where his true sympathies lay. At least a dozen would-be assassins failed before Catholic partisan Francois Ravaillac finally succeeded in 1610. Fearing the king intended to wage war on the Pope, Ravaillac stabbed King Henry while his carriage was caught in a traffic jam on the streets of Paris.

But this was far from the last indignity that Henry IV was to suffer. In 1793, French revolutionaries all hopped up on liberté, égalité, and fraternité decided to break into the royal graves in Saint-Denis Cathedral and mutilate the corpses. Henry reportedly suffered a case of being separated from his head.

In 2010, a team of mostly French scientists and historians said they’d identified an embalmed head in a private collection as Henry’s, based on various forensic techniques. The head contained several distinguishing features that correlated with portraits of the monarch: a healed bone fracture matching the location of a stab wound from a previous assassination attempt and a dark spot above the right nostril. They reconstructed the face of the head based on the shape of the skull, and found it to be consistent with both the king’s portraits and death mask. Plus, radiocarbon dating confirmed that the head hailed from around the 1600s. A paper outlining their findings appeared in the Christmas issue of the British Medical Journal that year.

At the time, critics noted that the authors had failed to provide the most rock-solid of identification techniques: DNA evidence. In 2012, one of the authors, forensic pathologist Philippe Charlier, seemed to have found a DNA connection. Charlier and Spanish geneticist Carles Lalueza-Fox linked DNA from the head to DNA found on a bloody rag stored in a decorative gourd. But this wasn’t just any old bloody rag stored in a decorative gourd; legend had it that the rag was a handkerchief that had been used to mop up blood from a freshly guillotined Louis XVI in 1793. The two scientists isolated some Y chromosome – the genetic material passed down through the paternal line – from both the cloth and the head, and said there was a match. Louis was a direct descendant on an unbroken male line from Henry.

But the French historian Philippe Delorme was still skeptical, mostly because there was so little Y chromosome lingering in the head. The match could have been a product of chance. Delorme and geneticist Jean-Jacques Cassiman rounded up three living descendants of the House of Bourbon (the French royal line that included both Henry IV and Louis XVI) and took blood samples. The Y-chromosomes of the modern Bourbons bore no relation to the Y-chromosomes of the head or the rag. Thus, Delorme and his team wrote in the European Journal of Human Genetics earlier this month, neither sample was from a French king.

In the wake of Delorme’s DNA study, some of the authors of the original paper wrote to the BMJ this week and called for the journal to retract their study.

"Robust scientific arguments recently published negate the conclusions of the studies carried out by Charlier" and colleagues, the detracting authors wrote. "A rigorous scientific anthropological study should have excluded the hypothesis (and the findings) that the head belonged to Henri IV."

But lead author Charlier stands by his work. In comments made to the news website Phys.org, he said the Bourbon family tree was complicated by possible philandering, which could explain why DNA from the samples’ failure to match the modern descendants.

"It is hopeless to try to match a family tree and a series of genetic links (over) such a long period," Charlier wrote in an email to Phys.org.

Charlier says that he has a forthcoming paper that provides an exact match between Henry IV’s death mask and a three-dimensional reconstruction of the ancient head. The head itself, he says, is in a bank vault in Paris, destined for reburial.

But if that head isn’t King Henry’s, where did the real one get to? Actually, it might still be with his body. While the revolutionaries were known to have ransacked royal graves, there’s no solid proof that Henry IV was one of their post-mortem victims. The regal tombs were sealed up again in the early 1800s, so unless scientists manage to get approval to unseal the graves, the mystery will likely linger.