Mr. Hagan, who turned 69 in jail on Tuesday, was a militant member of the Nation of Islam on Feb. 21, 1965, when Malcolm X was shot while giving a speech at the Audubon, in Washington Heights. Mr. Hagan, then known as Talmadge X. Hayer, was captured by the crowd and shot at and beaten before being rescued by the police.

Image Thomas Hagan in an emergency room after shooting Malcolm X at the Audubon Ballroom in Manhattan on Feb. 21, 1965. Credit... Associated Press/New York Daily News

Two other men, Muhammad Abdul Aziz (then known as Norman 3X Butler) and Kahlil Islam (then Thomas 15X Johnson), were also charged with the murder. They maintained their innocence. Mr. Hagan did not, testifying at his trial in 1966 that he was responsible for the murder and that his co-defendants were innocent.

All three men were sentenced to 20 years to life.

Mr. Hagan said in a 1977 affidavit that he and several accomplices (not Mr. Aziz or Mr. Islam) decided to kill Malcolm X because he was a “hypocrite” who had “gone against the leader of the Nation of Islam,” Elijah Muhammad. Mr. Hagan said that after one man shot Malcolm X in the chest with a shotgun, he and another man fired several more rounds at him.

Mr. Aziz was paroled in 1985, and in 1998 was named by Louis Farrakhan to be chief of security for the Harlem mosque that Malcolm X once headed. Mr. Islam was paroled in 1987.

Mr. Hagan, who earned a master’s degree while in prison, according to a 2008 profile in The New York Post, was placed on work release in 1988. In 2008, he was spending his free days with his wife and children in Sunset Park, Brooklyn, and working in a fast food restaurant.