In each of these interviews, we asked the principal players not only to tell their stories, from start to finish, but also to provide us with primary source documents, such as emails or memos, even if they shared them on the condition that we could not reproduce them. Documents are better than human memory: They nail down names and days and times — some of the last captured emails offered windows into how various email accounts were cracked open — and sometimes give us a sense of contemporaneous reactions. The Democratic Party officials were surprisingly open to telling this story, as they almost all felt that the media had focused far too much on the content of the stolen emails themselves and not nearly enough on how the 2016 election had been disrupted by a Russian plot. The White House didn’t want to discuss the topic.

Kitty Bennett’s original chronology grew in length, as we filled it in based on our interviews and collected documents, ultimately reaching more than 10,000 words: a 28-page compilation of people and events that served as the core of our narrative.

It was while doing all these interviews that we first heard the story of Yared Tamene, the tech-services consultant at the D.N.C. who had fielded a call in September 2015 from an F.B.I. special agent named Adrian Hawkins — who contacted the D.N.C. to disclose that federal officials had evidence that the D.N.C. computer system had already been hacked. But Mr. Tamene did not believe he was talking to a real F.B.I. agent, so he didn’t move definitively to find and shut down this intrusion.

Even after Special Agent Hawkins repeatedly called Mr. Tamene and finally met with him in person last January, he remained skeptical, describing their encounter this way in an internal D.N.C. memo: “During this meeting, SA Hawkins showed his FBI badge to us, and shared his business card, lending some credence to his claim about working for the FBI.” This was five months after the F.B.I. had first contacted the D.N.C. But Special Agent Hawkins’s superiors took no steps to independently reach out to the committee’s leaders to persuade them to take seriously what appeared to be a Russian government attack. Between the passivity of the F.B.I. and the passivity of the D.N.C., almost no progress had been made to identify and lock out the hackers.

Mr. Tamene never agreed to speak with us, although we happened to run into him during one of our visits to D.N.C. headquarters. But based on documents we reviewed — including an internal D.N.C. account of his dealings with the F.B.I. that Mr. Tamene himself had written — we were confident we had found our patient zero. Our story would start in September 2015, when this first warning call had come in from the FBI.

When you do reporting like this, you begin to hear the same stories over and over again, told by different players who experienced the same events. These accounts might seem redundant. But for reporters, they’re vital stuff, because each person fills in different tidbits — or pieces of color, as we call them. These overlapping stories help increase your confidence that the version of events you’re piecing together is fair and true, particularly when backed up with emails and other documents.

While I was focused on the D.N.C., David was busy pressing Obama administration officials to explain how they responded to the cyberattacks — a time-consuming process because of the difficulty of getting access to them and, in some cases, because of their reluctance to talk. David is perhaps the best-sourced cybersecurity reporter in the United States: He was the guy who broke the story of the most sophisticated cyberattack in history, the American-Israeli attack on Iran’s nuclear facilities. (That tale recently became a documentary.) Eventually the White House began to tell its story, and it’s no surprise that when President Obama gave his news conference on Friday, his version of events echoed what we had already reported.