Malcolm X's family plans to sue the FBI, CIA and New York City police for $100m (£82.6m) in damages over the assassination of the US civil rights activist exactly 58 years ago on Tuesday.
His daughter Ilyasah Shabazz has accused several federal and New York government organisations of fraudulently concealing evidence, saying that they "conspired to and executed their plan to assassinate Malcolm X".
"For years, our family has fought for the truth to come to light concerning his murder," Ms Shabazz said at a news conference at the site of her father's assassination, now a memorial to Malcolm X.
Malcolm X rose to prominence as the national spokesman of the Nation of Islam, an African-American Muslim group that espoused black separatism.
He broke away from the group in 1964 and moderated some of his earlier views on racial separation, which angered Nation of Islam members and resulted in death threats.
He was aged 39 when he was shot dead on 21 February 1965 on stage by three gunmen as he prepared to speak at the Audubon Ballroom in Manhattan.
Ms Shabazz, then just two years old, was present with her mother and sisters.
Associates of Malcolm X said after the shooting that they believed several government agencies were aware of the assassination plan and allowed it to happen.
A Nation of Islam member, Talmadge Hayer, confessed in court to being one of the assassins.
But a New York state judge threw out the convictions of two other men in 2021 who wrongly spent decades in prison for Malcolm X's murder.
The two men were exonerated at the request of the Manhattan district attorney's office, which said an investigation had found that prosecutors and law enforcement agencies withheld evidence that, had it been turned over, would likely have led to the pair's acquittal.
New York law requires a notice of claims to be served on certain government agencies before a lawsuit is filed.
The NYPD said it would not comment on pending litigation. The FBI and the CIA did not immediately respond to requests for comment.