When the call came asking him to take on one last big assignment, the then-74-year-old Walsh said yes, embarking on a six-year journey digging into the crimes of Iran-Contra.
His detractors — and there were many — said his seemingly unending investigation was a clear case of prosecutorial abuse.
Iran-Contra paled in comparison to the Watergate scandal that brought down President Richard M. Nixon. But both were Washington spectacles: a collision of the executive and legislative branches of government, televised congressional hearings, a presidency in peril, an alleged criminal cover-up and criminal prosecutions that were, in Iran-Contra, all overseen by Walsh.
"I found myself at the center of a constitutional maelstrom," Walsh wrote in his 1997 book, "Firewall: The Iran-Contra Conspiracy and Cover-up."
Walsh "was really guided by a sense of intense personal responsibility for trying to do the right thing," said one of his former prosecutors, Michael Bromwich.
"For all the baseless charges that he was political and all through the many frustrations, he took his public service incredibly seriously and at great personal cost. His wife was quite ill. He had this killing schedule and he gutted it out. That's a level of sacrifice we don't have a right to expect from people called to public service. But it's the level of effort and sacrifice he was willing to give. He was truly a patriot and he was truly offended by corruption he saw at high levels in the U.S. government."
Iran-Contra involved two covert operations directed from the Reagan White House. In both, Congress was kept in the dark. The first operation was the secret supplying of weapons to rebels in Central America who were seeking to overthrow the leftist government of Nicaragua. At the time, Congress had prohibited U.S. military aid to the Contra rebels.
The second operation was the secret sale of arms to Iran in an effort to free U.S. hostages held in Lebanon. Iran was thought to possess some influence over the hostage-takers. The White House linked the two operations by secretly diverting millions of dollars from the Iran arms sales into buying guns for the rebels in Central America.
The disclosure of the diversion triggered a political firestorm, leaving the Reagan administration with little choice but to call for a criminal investigation by a wholly independent prosecutor. As a court-appointed independent counsel selected by three federal appeals judges, Walsh was given a broad mandate to pursue wrongdoing.
Walsh's investigation was a two-phase undertaking.
First, he prosecuted key figures, including former Marine Lt. Col. Oliver North, national security adviser John Poindexter and private-sector operatives who helped move missiles to Iran and guns to the Contras.
Eleven people pleaded guilty or were convicted by juries in Iran-Contra, but the two biggest courtroom victories for Walsh's prosecutors — convictions of Poindexter and North — were overturned on appeal.
Congress granted both men limited immunity from prosecution in exchange for their testimony in nationally televised hearings. The congressional immunity deals spelled the death knell for both criminal cases.
Critics urged Walsh to end the probe.
"To me, the real mark of Judge Walsh in terms of his courage and his commitment to public service was that he chose after that first phase not to simply say, 'We're done, I'm leaving,' but to complete the task that had been assigned to him," said Craig Gillen, a prosecutor on Walsh's team. "All of that information obtained in that second phase would simply not have been known to the country and history if it had not been his willingness to persevere."