Seventy-three years ago, on Monday, Adolf Hitler killed himself in his Berlin bunker alongside his wife of one day, Eva Braun. With the Red Army closing in, their bodies were hastily burned and buried in a shell crater in the nearby garden.

That’s the official story anyway.

Hitler was alone in his study with Braun when they died by suicide. Only a handful of Nazis saw the bodies before they were wrapped in gray blankets and moved to the Chancellery garden to be cremated. Two of the witnesses, the new Chancellor Joseph Goebbels and Hitler’s private secretary, Martin Bormann, killed themselves in the following days. The small number of surviving people who actually saw the bodies or material evidence is one reason for the range of various conspiracy theories that have persisted over the years: that Hitler did not die in Berlin but fled to the South Pole or Japan, that he died in 1962 in Argentina, in 1971 in Paraguay or in 1984 in Brazil.

In an effort to definitely put these theories to rest, two investigative journalists, the French Jean-Christophe Brisard and the Russian-American Lana Parshina recently carried out an investigation whose results were published in France last month as a book (La mort d’Hitler) and television documentary (Le mystère de la mort d’Hitler.) An English translation is scheduled to come out in September.

Brisard and Parshina, who is also the director of a documentary about the reclusive daughter of Josef Stalin, Svetlana About Svetlana, based their research on the examination of still-classified documents about the last days in the bunker and the discovery and the authentication of the bodies of Hitler and Braun, preserved in the State Archive of the Russian Federation, in the vaults of the FSB (the Russian intelligence service, heir to the KGB), and at the Russian State Military Archive.

As the centerpiece of their investigation, they analyzed, with the help of Philippe Charlier, a French scientist who specializes in historical “cold cases,” two bone fragments in the Russian government’s possession long believed to belong to Hitler: a skull fragment with a bullet hole preserved in a floppy-disk storage box in the State Archive, uncovered in 1993 and displayed to the public as part of an exhibition in 2000, and a jawbone stored in a cigarillo box in the FSB archives. Their findings are confident, if unspectacular: They cannot prove with only a visual analysis that the fragment of skull is or is not Hitler’s (“It belongs to an adult. Period,” says Charlier) but are sure that the jawbone is.

Charlier’s previous studies, involving alleged remains of French king Henry IV and the revolutionary leader Robespierre, have been subject to controversy. In the case of Hitler’s skull, his findings support those from the early 1970s by an American scholar, Reidar F. Sognnaes, with a Norwegian colleague, Ferdinand Ström. Sognnaes and Ström did not have access to the actual jawbone and relied on testimonies of Hitler’s dentist and physicians, X-ray plates taken after a 1944 assassination attempt, and findings of the Russian autopsy to assert that “Hitler did in fact die, and that the Russians did indeed recover and autopsy the right body.”

“Now he’s had it. Pity we couldn’t take him alive. Where’s the corpse?” — Josef Stalin

Charlier analyzed the teeth with a stereo microscope and was even able to dissect a few particles he involuntarily brought back with him in France, stuck to his laboratory gloves, and concluded that the jawbone presented to him is not a “historical forgery.” He asserts: “We are certain of the anatomical correspondence between the radiographies, the descriptions of the autopsies, the tales of the witnesses, especially those who made these dental prostheses, and what we had in hands.” Brisard and Parshina add, with similar confidence: “We can state that Hitler died in Berlin on April the 30th, 1945. Not in Brazil at 95, nor in Japan, nor in the Argentinian Andes. The proof is scientific, not ideological. Coldly scientific.”

To obtain access to the archives, the two authors write that they had to endure “months and months of unending negotiations, repeated demands expressed by email, by mail, by phone, by fax (yes, often still in use in Russia), in person with stubborn civil servants.” The description of their investigations makes for a lively tale, full of appointments not honored, rude secretaries, and unexpected twists, like the purchase of a bottle of Armenian cognac to mollify an archivist or a visit to a storage room where all oxygen is expulsed at night to trap any illegal visitors. But the most interesting lesson is elsewhere: Their book describes how the death of Hitler, for more than seven decades and counting, became a cold case with ideological implications during the Cold War.

As the British historian Antony Beevor wrote in 2002 in his book Berlin: The Downfall 1945, “the whole question of Hitler’s fate had begun to assume immense political significance before the facts were clear.” The first political strife was internal to the Soviet Union state, as the question of Hitler’s death became caught up in a power struggle between Stalin’s military and interior ministries.

The fate of the bodies was symbolic of this strife. On May 5, a unit of the Smersh, the counterintelligence organization of the Red Army, dug up the cremated remains, including the jawbone preserved today in the archives, and kept them from the 5th Shock Army, supposedly in control of the bunker zone. Written at the end of May by Aleksandr Vadis, a unit leader of the Smersh, the first report on the death of Hitler was based on the testimonies of Harry Mengershausen, a member of Hitler’s personal guard, and Käthe Heusermann, the assistant of the dictator’s dentist, who identified the jaw presented to her as Hitler’s. The report assumed that the deaths were caused by cyanide ingestion.

The jawbone, the decisive proof, was brought to Moscow. The rest of the remains were reburied at the beginning of June 1945 in secret by the Smersh 50 miles west of Berlin at Rathenow. They would be dug up again a few months later, at the beginning of 1946. Anxious to keep them at hand, the Smersh exhumed the corpses of Hitler, Eva Braun, Joseph Goebbels, his wife, their six children, and Hans Krebs, the chief of staff of the German army, and buried them again in Magdeburg, near its headquarters in the Russian occupation zone of East Germany. In 1970, when the Magdeburg base was returned to East German control, then KGB director and future general secretary of the communist party Yuri Andropov asked that the remains be destroyed.

Then there’s the story of the skull. A few days before the Nazi collapse, Otto Günsche, Hitler’s bodyguard, was captured by the NKVD, the Soviet interior ministry, and said that his former boss shot himself in the head. NKVD chief Lavrenti Beria hated his rivals in the Smersh and saw an opportunity to discredit them by casting doubt as to whether they had autopsied the right bodies. At the beginning of 1946, the NKVD initiated the “Operation Myth,” which involved harsh interrogations, often carried in the middle of the night, of all the occupants of the bunker they could find, including Günsche and also Heinz Linge, Hitler’s valet, and Haus Baur, his personal pilot. Their testimonies converged, with several discrepancies, on the theory of a death by gunshot. The operation also led to new excavations near the Führerbunker and the discovery in May 1946, 20 inches deep, of a skull fragment with a bullet hole. The death by shooting theory revolves around the skull.

Cold War paranoia played a major part in the ambiguity around Hitler’s death. Stalin himself never seriously doubted the suicide of his archenemy (“Now he’s had it. Pity we couldn’t take him alive. Where’s the corpse?” he reportedly asked when informed of Hitler’s death by Gen. Georgy Zhukov), but the Soviets tried to keep their allies in the dark on that matter. On May 2, 1945, the state news agency Tass said that the announcement on German radio of the reports of Hitler’s death were a “fascist trick to cover [his] disappearance from the scene.” On May 26, Stalin told U.S. Ambassador W. Averell Harriman and President Harry Truman’s envoy, Harry Hopkins, that he thought Hitler did not die but fled with his private secretary, Martin Bormann; Goebbels; and Krebs, and asserted the same opinion 10 days later, even pressuring Zhukov to say to the international press that Hitler “could have left Berlin by air at the last moment.” By keeping the Allies ignorant and spreading the rumor that Hitler might have fled to the Western Hemisphere, the Soviets hoped to force them to launch a costly and useless intelligence operation.

After the end of the war, the Soviet Union held the witnesses of Hitler’s last hours in secret captivity, only transferring them to Germany 10 years later, “at a time when the Western intelligence services had obtained on their own confirmation of the death of the dictator. But even then, Moscow was still arguing that Hitler did not shoot himself but took one of the cyanide capsules Heinrich Himmler gave him, which he had tested on his dog Blondi—the death of a coward, conforming to the wishes of the Soviet propaganda. This theory was put forward in a book published in English in 1968 by a former Red Army interpreter, Lev Bezymenski. One of the most respected Hitler scholars, Ian Kershaw, described Bezymenski’s efforts in 2001 as an example of “the intentionally misleading account of Hitler’s death by cyanide poisoning put about by Soviet historians … [that] can be dismissed.” The cyanide story was also challenged in 1993 when the Russian newspaper Izvestia revealed the existence of the skull fragment with the bullet hole, conserved in a cardboard box with the inscription “blue ink, for fountain pens.” The information was quickly confirmed by the Russian State Archive, which, shortly after the Soviet collapse, was eager to show more openness than its predecessors.

The Cold War was then over, but a cold case continues: The “Great Patriotic War” remains a central theme of Russian nationalism in the Putin era, and the government is still sensitive to allegations that Hitler escaped their grasp.

Russian history, and the way Western countries see it, is a sensitive topic. Brisard and Parshina’s investigations took place between the beginning of 2016 and the end of 2017, at a time when relations between Russia and the West were rapidly deteriorating over the crises in Syria and Ukraine as well as new allegations of election meddling.

When the authors requested permission to examine the remains of Hitler, the head of the State Archive answered: “By the way, who would do the analysis? Find someone scientifically irreproachable and not an American. Especially not an American.”

There was reason for their suspicion. In 2009, Nicholas F. Bellantoni, an archeologist at the University of Connecticut, claimed he had analyzed a sample of the skull in a documentary broadcast on the History Channel, bluntly titled Hitler’s Escape, and concluded that it belonged to a 40-year-old-woman—but probably not Eva Braun, who poisoned herself. His findings gave another impulse to the Hitler-did-not-die-in-the-bunker cottage industry, exemplified by Jerome R. Corsi, the far-right American writer who, in addition to peddling theories about Barack Obama’s birthplace, is the author of Hunting Hitler: New Scientific Evidence That Hitler Escaped Nazi Germany. Corsi claimed that Bellantoni’s work convinced him that “politically correct authorities” preferred to “invent a lie, canonizing the Hitler suicide story as the official version to avoid explaining their malfeasance to their citizens back home who were demanding justice for horrendous crimes Hitler had committed against humanity.” All of that despite the fact that Bellantoni, whose conclusions about the skull are hence far too assertive according to the French investigation, himself said in 2012 that he thought Hitler “didn’t escape; he clearly died in the bunker. … Because the skull plate was not him doesn’t mean that he didn’t die in the bunker, it simply means what they recovered was not him.”

The Russian State Archive had then claimed, and still claims, that Bellantoni never got access to its vaults. Both he and that History Channel say he did. Russia’s wariness about letting the French team examine the skull may have been caused by fear they would come to the same conclusion as Bellantoni. To ask if the skull preserved in the State Archive is or is not Hitler’s, write the authors, “means talking politics, discussing the official position of the Kremlin. An unthinkable option for the head of the Archive. Absolutely unthinkable.” When they question the FSB, a civil servant asks Lana Parshina, who obtained a green card in 1997 and has since become an American citizen: “Which side are you on? Are you Russian or American? You are like all these American journalists who refuse to believe we were the first to find Hitler. You are looking for a scoop.” But at another moment, in the State Military Archive, a staff member blatantly leaves the room for a few minutes to let the authors read files they are not supposed to, and another, at the Ministry of Foreign Affairs, informed that they have brought home particles of Hitler’s jawbone, writes to them, in French, that they won’t be “prosecuted” if their findings “do not clash with the official position of Russia.”

That’s why the authors have the honesty, at one moment, to assess the possibility that they might be manipulated: “Why the FSB would hand us secrets so well kept since more than seventy years? Why us? … And if letting us consult the archives about the death of Hitler served the Russian propaganda?” At the last page of the book, Jean-Christophe Brisard asks Lana Parshina what would have happened if they had concluded Hitler’s teeth were not Hitler’s. She answers, calmly: “That would have been a huge problem for Russia.”