"The public must be satisfied that Oswald was the assassin; that he did not have confederates who are still at large," Katzenbach wrote.
Four days after the memo, Johnson appointed some of the nation's most prominent figures to the Warren Commission, which ultimately concluded that Oswald acted alone, a theory still disputed. Skeptics and conspiracy theorists have often cited Katzenbach's memo as a sign of a government cover-up.
In February 1965, Johnson picked Katzenbach as his attorney general, but he held the post for less than two years, feuding with FBI Director J. Edgar Hoover and others before stepping down in October 1966. A short time later, he was named an undersecretary of state, a post he held for the remainder of the Johnson administration and which led to an unhappy entanglement with the Vietnam War.
In testimony before the Senate's Foreign Relations Committee in 1967, Katzenbach made a controversial defense of the war's legality, citing the 1964 Gulf of Tonkin resolution, which allowed the U.S. to repel attacks and prevent further aggression. The committee's chairman, Sen. J. William Fulbright, had disputed that the Tonkin resolution — passed before the U.S. had sent ground troops to Vietnam — was a formal declaration of war.
"What could a declaration of war have done that would have given the president clearer authority?" Katzenbach responded. "It would not, I think, reflect correctly the very limited objectives of the United States with respect to Vietnam to use an outmoded phraseology, to declare war."
Katzenbach believed his testimony was accurate, but acknowledged its unpopularity. Philip Roth and Jules Feiffer were among the artists who took out a full-page newspaper ad condemning his remarks. Sen. Eugene McCarthy of Minnesota would cite Katzenbach as a reason for running for president in 1968 as an anti-war candidate, a decision that helped convince Johnson not to seek a second term.
In 1969, after the Johnson administration ended, Katzenbach was appointed IBM's general counsel and helped represent the computer giant in its long fight against an anti-trust lawsuit filed by the government and eventually dismissed. He also served on prison reform panels and remained active in national Democratic politics and constitutional issues. In December 1998, he took part in a protest in Princeton against Republican efforts to impeach President Clinton and also spoke as a witness for the president.
Nicholas deBelleville Katzenbach was born in Philadelphia in 1922 to a family of politicians. His middle name, with the unusual abbreviation deB., came from a forebear who had served as physician to Napoleon's brother before emigrating to the U.S.
Katzenbach served in the Army Air Force during World War II and spent two years as a prisoner of war in Italy. He later graduated from Princeton and the Yale Law School and studied at Oxford University for two years as a Rhodes Scholar.
For much of the 1950s, Katzenbach was a professor of law, first at Yale, then at the University of Chicago. He was on a leave of absence, in Switzerland, when John F. Kennedy received the Democrats' nomination for president, in 1960.
His eight-year career in presidential administrations started the following year.
It was an exciting time," Katzenbach told the AP. "There were lots of young people who got themselves involved in civil rights, and later in protesting the Vietnam War, feeling involved in the government and what's going on in their own future. To my mind that's what makes this a great country."
AP National Writer Hillel Italie contributed to this report.
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