Muhammad Aziz, one of the two men who last month were exonerated in the 1965 killing of civil rights leader Malcolm X, sued New York State on Tuesday for at least $20 million in damages, saying his imprisonment had caused “deep and lasting trauma”.

Last month, a judge exonerated Aziz, 83, and Khalil Islam, two of the three men convicted of the killing. Manhattan District Attorney Cy Vance had found after an almost two-year investigation that authorities withheld evidence in the trial of Aziz and Islam, the New York Times reported.

Aziz and Islam always maintained their innocence in the assassination. Islam died in 2009 but Aziz continued to fight to clear his record. “While I do not dwell on what my life might have been like had this travesty of justice never occurred, the deep and lasting trauma it caused cannot be overstated,” Aziz said in a statement on Tuesday announcing the lawsuit.

“Those responsible for depriving me of my liberty and for depriving my family of a husband, a father, and a grandfather should be held accountable,” he said.

Aziz has made it known to New York City that he plans to sue it for $40 million unless an agreement on damages is made within 90 days. His lawyers said they would file similar lawsuits on behalf of the family of Islam. The lawsuit is the first action taken by Aziz to receive monetary relief since his record was cleared and “represents a modicum of compensation for the destruction wrought by this grievous miscarriage of justice,” according to the lawsuit.

Malcolm X was speaking at an Organization of Afro-American Unity event at Manhattan’s Audubon Ballroom on February 21, 1965, when a group of men suddenly rushed to the podium and fatally shot him several times. Three members of the political and religious group the Nation of Islam were arrested — Islam, then known as Thomas 15X Johnson; Aziz, then known as Norman 3X Butler; and Mujahid Abdul Halim.

They were held responsible for the shooting and sentenced to life in prison in 1966. Halim admitted to playing a role in the assassination but maintained that Aziz and Islam were not involved in it, according to the Innocence Project.

Halim in 1978 disclosed his co-conspirators in the assassination. He identified four other men he said were involved. However, a judge at the time rejected a motion to vacate Aziz’s and Islam’s convictions, the Innocence Project said.

Vance opened an investigation into the case following a Netflix documentary series last year titled “Who Killed Malcolm X?” that raised doubts about the convictions. Vance’s investigation found that key physical evidence and documents were lost over the years. What is more, many investigators, witnesses and potential suspects have since died and the murder weapons could no longer be tested, The New York Times reported.

FBI documents also included information that implicated other suspects and “pointed away” Aziz and Islam, The New York Times added.

“This points to the truth that law enforcement over history has often failed to live up to its responsibilities,” Vance told the Times. “These men did not get the justice that they deserved.”

Recently, a confession letter written by a former Black New York Police Department (NYPD) cop on his deathbed was released. The letter alleged that the department and the FBI played a role in the assassination of Malcolm X. In the letter that was obtained by ABC News, Ray Wood, who reportedly worked as an undercover police officer on the day Malcolm X was assassinated, confessed he “participated in actions that in hindsight were deplorable and detrimental to the advancement of my own black people.” The letter was written on January 25, 2011.

Wood claimed he was recruited by the NYPD in 1964 to “infiltrate civil rights organizations” for the sole purpose of digging up evidence of criminal activity to enable the FBI to taint the image of their followers and arrest their leaders.

Days before Malcolm X was fatally shot, Wood claimed his handler arranged the arrest of two of his “key” security guards in a bid to leave a gaping hole in the civil rights activist’s security apparatus.

“It was my assignment to draw the two men into a felonious federal crime, so that they could be arrested by the FBI and kept away from managing Malcolm X’s door security on February 21, 1965,” Wood wrote, adding: “… At that time I was not aware that Malcolm X was the target.”