Before last November’s presidential election, a half-dozen former FBI agents told me that Donald Trump was questioned by the FBI about his business dealings on numerous occasions since the early 1980s. But the agents couldn’t recall the details.

So together with MIT doctoral student Ryan Shapiro, I filed a Freedom of Information Act (FOIA) request for all FBI records on the Trump Organization, Trump Entertainment Resorts, Trump University, and the Trump Foundation. When the FBI failed to respond, we sued, and the bureau turned over dozens of pages of documents.

One set stood out. It was heavily redacted, but it contained bits and pieces of a wild story about a person who told the FBI that he got a menacing phone call from a man with a thick New York accent who threatened his family. Intriguingly, the documents stated that the call came from a New York City phone booth across the street from the Ed Sullivan Theater, where Donald Trump was appearing that day as a guest on David Letterman’s show.

The person who received the call was identified only as “C” for “complainant.” But the FBI left behind several clues that helped us figure out that it was Kristopher Hansen, an attorney who represented a group of private investors in Trump Entertainment Resorts, who received the menacing phone call a day after the casino group filed for bankruptcy.