In the late Sixties Anthony Russo was a rumpled, shaggy-haired, left-wing radical whose role in the publication of the secret Pentagon Papers hastened the downfall of President Nixon. The White House “dirty tricks” response to the exposure of Defence Department secrets of the Vietnam War became inextricably linked to the Watergate scandal and helped to put the war on trial.

Russo stood in court as co-defendant with Daniel Ellsberg, a top Pentagon military analyst, charged with espionage, theft and conspiracy for leaking the papers. The case was dismissed after a ruling that the Government was guilty of misconduct by using a group of White House operatives to engage in an illegal burglary to find evidence to discredit Ellsberg. The same operatives were later caught breaking into the Democratic National Committee headquarters at the Watergate hotel complex in Washington in 1972.

Russo was a Rand Corporation researcher sent to Vietnam in 1965 for a study that included interrogating communist Vietcong prisoners of war. It was in Saigon that he first met Ellsberg, and Russo returned home convinced that the US was involved in an illegal war.

Ellsberg was similarly disillusioned, and the two met again three years later at the Rand Corporation. Russo recalled that Ellsberg had been a “total hawk” in Vietnam but later seemed shattered. “He was very tortured. There was no way he could justify the war any more.”

Ellsberg told him about a secret study of the origins of the Vietnam War which was commissioned by the Defence Secretary Robert McNamara. It provided evidence of lying by government officials, including several presidents, about the scope and purpose of the war, and showed that the US had falsely accused North Vietnam of an act of unprovoked aggression in the Gulf of Tonkin, which was used as justification for broadening US involvement in the war.

Russo urged Ellsberg to “turn over to the newspapers” the 47-volume Pentagon Papers. Ellsberg was originally shocked by Russo’s suggestion, but he eventually did so. His action was branded by Nixon as treason. Ellsberg said of Russo: “He was a courageous collaborator. I knew that he was the one person with the combination of guts and compassionate concern about the war who would take the risk of helping me.”

Ellsberg asked Russo if he knew where he could find a photocopying machine to print the papers. “And within an hour he got back to me with the word that his girlfriend had a machine in her Hollywood office he could use.” After several weeks of copying behind closed doors the documents were given to The New York Times, which published the first instalment — sparking an unprecedented and unsuccessful attempt by the Nixon Administration to prevent further publication.

Russo refused to testify against Ellsberg and was jailed for 45 days. A few days before Christmas both men were indicted. Once the trial was under way the two men clashed repeatedly on strategy: Russo wanted to radicalise the proceedings with anti-war activist witnesses but Ellsberg preferred to use more establishment figures.

The case was dismissed in May 1973 after the court learnt that a White House team had broken into the office of Ellsberg’s psychiatrist looking for evidence to undermine his character. The break-in team, who became known as the plumbers, were led by the FBI agent G. Gordon Liddy and the CIA officer E. Howard Hunt (obituary, January 25, 2007), who were later both arrested over the bungled Watergate break-in.

After the case Ellsberg became a hero of the antiwar movement, but Russo’s name and involvement in the affair were largely forgotten. Lee Boek, a friend of Russo, said that Russo “never felt he got the credit he deserved” for his role in publicising the Pentagon Papers. “He risked his life and his job. He suffered a lot for it,” he said. Ellsberg sought to give his former colleague and co-defendant his due. “The fact is I will be eternally grateful to Tony for his courage and partnership,” he said.

Anthony Russo was born in Suffolk, Virginia, in 1936. He studied aerophysics at Virginia Tech in the late 1950s before earning a scholarship to Princeton. During a foreign relations course in his third year he joined the Rand Corporation, specifically to work for them in Vietnam, but he was fired after his involvement in the Pentagon Papers affair.

After the trial he worked for the LA County Probation Department. He retired in the 1990s and moved to Suffolk where he continued as an activist for peace and an critic of the Iraq war.

Russo, who suffered from heart trouble, was married and divorced twice and had no children.

Anthony Russo, antiwar activist, was born on October 14, 1936. He died on August 6, 2008, aged 71