Two men convicted of gunning down United States activist and civil rights advocate Malcolm X nearly six decades ago, are to be cleared of the crime, according to a top New York law enforcement official.

The Manhattan District Attorney’s office will move on Thursday to throw out the convictions of Muhammad A Aziz and Khalil Islam in the killing of the Black leader, news outlets and the district attorney said on Wednesday.

Identified by witnesses as two of the gunmen involved in the assassination, Aziz, then known as Norman 3X Butler, and Islam, then known as Thomas 15X Johnson, had long maintained their innocence.

"These men did not get the justice that they deserved,” Manhattan District Attorney Cyrus R Vance Jr told The New York Times newspaper in an interview after completing a lengthy reinvestigation of the case together with the Innocence Project and civil rights lawyers.

Vance tweeted on Wednesday his office would move to "vacate the wrongful convictions of two men” with "more to come tomorrow”.

One of the civil rights era’s most controversial and compelling figures, Malcolm X rose to fame as the Nation of Islam’s chief spokesperson, proclaiming the Black Muslim organisation’s message at the time: racial separatism as a road to self-actualisation. He famously urged Black people to claim civil rights "by any means necessary”.

He spent more than a decade building the Nation of Islam before becoming disillusioned and breaking acrimoniously with it in 1964, about a year before he was gunned down in New York City on February 21, 1965.

Aziz, Islam and a third man, Mujahid Abdul Halim – known at the time of the killing as Talmadge Hayer and also as Thomas Hagan – were convicted of murder in March 1966 and sentenced to life in prison.

The Manhattan investigation of the original case found prosecutors withheld evidence from the jury that pointed to other suspects and likely would have led to the acquittal of Aziz and Islam.

"This wasn’t a mere oversight,” Deborah Francois, a lawyer for the men told the Times. "This was a product of extreme and gross official misconduct.”

Hagan said he was one of three gunmen who shot Malcolm X, but he testified that neither Aziz nor Islam was involved.

Aziz, now 83, was released from prison in 1985. Islam was released in 1987 and died in 2009, according to the Times.

Malcolm X was killed in front of his wife and children as he began to address an audience of about 400 people at the Audubon Ballroom in the Washington Heights neighbourhood of Manhattan.

A man with a sawn-off shotgun rushed the stage and shot Malcolm once in the chest. Two others with semi-automatic pistols charged forwards, firing at him. He was pronounced dead at a nearby hospital with 21 gunshot wounds.

His funeral in Harlem was attended by leading Black civil rights leaders and as many as 30,000 mourners in the streets.

Historians and scholars had contended that the wrong men were convicted. Vance’s office said last year it would review the case.

In February, a letter came to light written by ex-undercover New York policeman Raymond Wood alleging the NYPD and FBI had covered up details of the assassination.

llyasah Shabazz, one of Malcolm X’s three daughters, said at the time the new accusations should prompt further investigation.

"Any evidence that provides greater insight into the truth behind that terrible tragedy should be thoroughly investigated,” she said.

In 2020, a six-part documentary series titled Who Killed Malcolm X? that streamed on Netflix had raised doubts about Aziz and Islam’s guilt and spurred New York authorities to revisit the case.