In early June of 1971, Ellsberg, who had left RAND and was working as a senior research fellow at M.I.T., hosted a small dinner party at his home in Cambridge. Ellsberg, who was then forty, had never met Alperovitz but invited him after a colleague said that they shared an intense opposition to the war. The Harvard graduate student was there as well.

Alperovitz had worked in the U.S. government on foreign affairs from 1961 to 1966—first in Congress, then at the State Department—and it was there, as an insider, that his opposition to the war hardened. As a Senate aide, in 1964, Alperovitz worked unsuccessfully to stop what he still calls the “phony” Gulf of Tonkin resolution, which allowed President Lyndon B. Johnson to escalate America’s military involvement in Vietnam. More than anything, the congressional vote confirmed his view that the war was a fraud perpetrated on the American public.

At the dinner, Alperovitz and Ellsberg, a former Marine and Pentagon analyst, talked about Nixon, liberal activism, nuclear weapons, and, of course, Vietnam. The top-secret papers never came up. But, as the party wrapped up and Alperovitz walked to his car, the Harvard graduate student pulled him aside and made a cryptic comment about some sensitive material on Vietnam and “boxes and boxes of papers,” Alperovitz recalled.

A day or two later, the graduate student arranged to meet Alperovitz at a park, she told me in an interview. She explained to Alperovitz that Ellsberg had entrusted her with thousands of pages of the documents, and that she had stashed them in cupboards in the pantry of her small apartment. Ellsberg had given copies of the papers to a Times reporter several months earlier, but had not heard from him since. She and Ellsberg didn’t know when the newspaper might run the story, or if it even intended to do so, and were eager to distribute more of the papers to other news outlets. “I needed help to do this work,” the woman told me, and Alperovitz seemed like “exactly the right person.”

When she asked Alperovitz if he would help, he immediately agreed. Decades later, Alperovitz said that his eagerness, despite the obvious risks, still puzzles him. “I’m a very cautious person, but I didn’t blink—which I don’t understand,” he told me. “I’m surprised I didn’t just say, ‘Whoops, I’m busy tomorrow.’ It was out of character.”

In a subsequent meeting with Ellsberg, Alperovitz mapped out a strategy. Ellsberg, who had tried to leak the secret papers to members of Congress but had been rebuffed, wanted to get all seven thousand pages of the papers out at once, if not in the Times then in the Washington Post or somewhere else. “My nightmare was that the F.B.I. would catch me and capture all the papers first,” Ellsberg recalled. He even considered using the Harvard Crimson’s presses to print the documents himself. Alperovitz talked him out of it. “I said to Dan, ‘Look, this is seven thousand pages of material, you’ll get one story, maybe two,’ ” Alperovitz said. “If you really want to get this out to the public, you’ve got to break it up and keep the story going.”

To Ellsberg’s surprise, the Times ran its first story on the papers several days later. The Nixon Administration quickly secured an injunction to halt publication. By then, Alperovitz was already working the pay phones around Cambridge and Somerville to contact a reporter from the Post and get more coverage. Days later, with Alperovitz acting as an intermediary, Ellsberg met with a Post reporter in a local motel room and gave him the entire secret report. After the reporter left, Ellsberg and his wife, who were hiding out in the motel, saw on television that F.B.I. agents had descended on their home to question him. For the next two weeks, the Ellsbergs remained holed up, with the Harvard graduate student taking the lead in finding new places to stash them. “I moved them every few days,” she recalled. “I’d call friends and say, ‘I need your apartment for two days, and I just want you to go somewhere else. Just don’t ask me any questions.’ ” Each time the couple moved, she crammed boxes of the secret history into her small Volkswagen and moved them along with the Ellsbergs.

The one time that Ellsberg knew whose apartment he was using, he said, was during weekend that he spent in Cambridge with a friend, Jeffrey Race, a fellow Vietnam veteran. Race recalled watching a television news report with his fiancée about the F.B.I. searching for Ellsberg. “They can’t find him,” Race told me, “and we joked that, ‘Hey, he’s lying right here in his underwear on the floor taking a nap in front of the TV.’ ”

It was at Race’s apartment that Ellsberg had his closest brush with arrest. At Ellsberg’s request, from a pay phone outside of Race’s apartment, Alperovitz called a friend of Ellsberg’s in Los Angeles to arrange a way for him to speak with his children and let them know that he was all right. As Ellsberg watched from the window, Alperovitz hung up and walked away. Minutes later, police cars converged around the phone booth. Ellsberg guessed that the F.B.I. must have been tapping his Los Angeles friend’s phone, or perhaps the pay phone, in their effort to find him. “We ducked behind the window,” Ellsberg recalled. “I’m thinking, Oh my God!” He and his wife left that same night for a different hiding place.

Alperovitz asked the administrator of the Cambridge Institute, the think tank he ran, to vacate her apartment for the Ellsbergs for several days. “It was a very matter-of-fact thing,” the administrator, Nancy Lyons, who is now retired and living in Concord, Massachusetts, said in an interview. She immediately agreed—she saw it as an opportunity to be involved in something larger than herself. “I might have just been naïve, but I didn’t have any hesitation.” The one concern she had, she told me, was that she had waited a long time to get the rent-controlled apartment, and she didn’t want to lose it if someone found out. (No one did.)

Alperovitz’s primary task was devising how to distribute the papers to as many news organizations as possible. Ellsberg usually told Alperovitz which newspapers to contact—the Boston Globe, the St. Louis Post Dispatch, the Los Angeles Times, the Christian Science Monitor, and the Detroit Free Press, among them—but he left it to Alperovitz to figure out the logistics.

Alperovitz told me that he improvised the elaborate handoffs. “I invented this stuff as I went along,” he said. “I don’t know how.” Getting journalists interested in the papers, then the most sought after documents in the United States, was easy. He would call a newspaper’s city desk from a pay phone, identify himself as Mr. Boston­—a code name that got a few references in “The Post”—and then offer to share some of the papers. “They were very happy to take them. Everyone wanted to be in on it,” he said.

The trickier part was handing off hundreds of pages of documents without being detected. Alperovitz and the Harvard graduate student recruited a handful of college students—all ardently opposed to the war—to help not only with mundane tasks, like getting the Ellsbergs’ groceries, but also to act as runners who delivered the papers.

During the frantic three weeks it took to distribute the documents, Alperovitz typically didn’t have time to even read all the papers before parcelling them out to reporters. He simply grabbed a few hundred pages, boxed them up, and sent the runners on their way. Alperovitz usually found out what was in each stack only when he read the news stories. The pace was so hectic that he and other participants have trouble remembering the exact sequence today. Alperovitz can’t remember, for instance, which reporter he called at the Cambridge hotel with instructions for finding the papers in the hallway. The former Harvard graduate student recalls a nighttime handoff of papers at an acquaintance’s home, but the details are hazy.