Who betrayed Anne Frank? Artificial intelligence could finally solve the mystery.
For nearly 75 years, some of the greatest investigative minds have tried to figure out who tipped off the Nazis about Anne Frank and the seven other Jews who were hiding behind a movable bookcase in Amsterdam.
Now, a former FBI investigator working with a production company hopes the decades-old mystery can be solved with the help of a new mind - an artificial one.
Vince Pankoke, who spent a chunk of his FBI career investigating Colombian drug cartels, has assembled a team of 20 researchers, data analysts and historians to look into what he calls "one of the biggest cold cases" of the 20th century.
The most unconventional member of his team is a piece of specialized software that can cross-reference millions of documents - police reports, lists of Nazi spies, investigative files for Frank family sympathizers - to find connections and new leads.
Proditione Media, a production company in the Netherlands, is soliciting donations to help fund Pankoke's investigation, which will become the subject of a podcast - and possibly a documentary.
The company, which asked Pankoke to lead the investigation, has also asked people with information or previously undisclosed documents to submit them on its website.
Already, the investigation has generated new interest - and new information, Pankoke said.
"The bottom line is until this day, there is nothing that's really held water or been definitive," he told The Washington Post. "The point of the investigation is fact-finding just to discover the truth. There is no statute of limitations on the truth."
Anne Frank's family spent more than two years in the secret annex at the back of her father's store. They were discovered on a summer day in 1944 and sent to concentration camps.
Before World War II was over, seven of the eight hiders were dead, including Anne, who died of typhus at age 15 at Bergen-Belsen camp in Germany.
Her father, Otto - the only person who hid behind the bookcase and survived - spent the rest of his life trying to figure out who tipped off the Nazis.
He also published his daughter's diary, which chronicled the rise of anti-Semitism in the Netherlands and has become required reading for students across the world.
He long suspected his family was turned in by Willem van Maaren, a recently hired employee who was not in on the secret behind the bookcase. Van Maaren was suspicious and would set "traps" to discover anyone in the office after hours.
In 1963, Otto Frank told a Dutch newspaper: "We suspected him all along."
Through the decades, others have been identified as potential betrayers, including a prominent Dutch Nazi by the name of Tonny Ahlers, and the wife of an employee who helped the Frank family hide.
The betrayer shouldn't have been hard to determine - the Nazis kept meticulous records - but the details surrounding the home in Amsterdam were believed destroyed in a 1946 bombing, making an easy identification impossible.
Investigations in 1947 and 1963 turned up nothing, and the identity of the Frank family's betrayer appeared lost to history.
But there are still reams of documents, including some that have been shipped to the United States and transferred to microfilm. That avalanche of information could be key to finding out how the Nazis learned about the Franks.
Anne Frank's Amsterdam was a maze of danger for the eight hiding Jews.
The annex where they lived could be seen easily from several nearby homes. A curtain accidentally left open or a loud noise at the wrong time could lead to discovery. They relied on counterfeit food-ration coupons to stay alive, operations that involved sympathetic collaborators and were heavily scrutinized by police.
Dutch officers were paid for every Jew they turned over to the Nazis, Pankoke said. They leaned heavily and sometimes violently on people suspected of helping Jews avoid the Nazis.
The hiders' collaborators had family members who could have tipped off police. Anne Frank chronicled moments when the people in the annex made mistakes that could have been seen by neighbors.
Pankoke believes all the investigative avenues haven't been explored.
He estimates it would take a human being a decade to go through all the documents and parse out possible connections. A computer designed by the big-data company Xomnia could process the same information in seconds.
"There is, of course, all possible types of administration done by the Germans of the time," Thijs Baynes, the filmmaker behind the project, told the Guardian. "And there is an even bigger circle of circumstantial evidence. What [Dutch Nazi party] members were in the neighborhood? What connections were with the Gestapo? Where were Gestapo agents living?
"To find that kind of information you have to go through millions of documents."
Pankoke is working to acquire more of those documents. He's spent the past few months squinting at microfilm in Amsterdam and at a National Archives facility outside Washington, trying to find relevant data.
He's also become an expert on previous investigations that sought Anne Frank's betrayer.
Pankoke started working for the FBI in the 1980s, spending his first four years as an agent in a small field office in Wisconsin. In 1992, he was transferred to Miami, where he helped build cases against Colombian cartels. After the Sept. 11, 2001, attacks, he was involved in FBI undercover operations, including cases that took him out of the country, he said.
He retired two years ago. But that didn't last long.
"Unfortunately, my wife is looking at me and saying, 'I thought we were going to be retired and taking cruises,'" the 59-year-old said, noting that his investigation could last into 2019.
Pankoke has always had a keen interest in World War II. His father and three uncles all served.
While in the FBI, he remembers driving by the Anne Frank House and marveling that no one had figured out who betrayed her family.
He said a small part of him realizes there may be no smoking gun. The key piece of data could have been destroyed. Or there may be heft to a recent report that says there was no betrayer at all, and that Anne Frank's discovery was an unfortunate coincidence.
That theory was posited in a research paper put out by the Anne Frank House itself.
Published late last year, the paper suggested that three men Otto Frank later identified as investigators weren't looking for enemies of Nazis, but were likely assigned to track down people committing ration card fraud or those dodging military service.
The museum's research is backed up by other historical documents, along with words written in Anne Frank's own hand: She talked about the arrests of men who had been caught dealing in illegal ration cards "so we have no coupons."
Such arrests were often reported to authorities, who regularly came across hiding Jews as they tried to sniff out people with phony ration cards.
In a statement this week, the Anne Frank House said it was keeping an open mind about Pankoke's research and has cooperated with his team.
"The background to and the exact details of the arrest of Anne Frank are issues that many people still find very compelling," the statement read. "We want to tell the life story of Anne Frank as completely as possible, so it is also important to take a close look at the raid that brought an end to the period in hiding."
It added: "Despite decades of research, betrayal as a point of departure has delivered nothing conclusive. . . . We are pleased that 'Cold Case Diary' is also carrying out research into the arrest and following new leads, and we are interested to see the results."
Pankoke told The Post his investigators have already made some discoveries.
They haven't identified Anne Frank's betrayers, but they've figured out who betrayed at least one other family that was hiding from the Nazis.
"It's because we're using artificial intelligence, because we're casting such a broad net," he said. "I know of one instance we've found - and we're looking hard at another one. We've only scratched the surface."
Eventually, he hopes to be able to show relatives of some victims the kopgeld (head price) receipt that a betrayer got for turning someone in. That, he said, would give their families something they haven't had before: closure.
Anne Frank, Pankoke said, "is a symbol of the youth and what the people who were in hiding went through. She's famous because she so eloquently documents this. But all of the other people who were in hiding, and their collaborators, they're just as important; they're just not as famous."