In a long overdue exoneration, two of the men convicted of the 1965 assassination of Malcolm X are expected to finally have their names cleared on Thursday—more than a half-century after they were accused of killing the civil rights icon.

Muhammad A. Aziz, 83, and the late Khalil Islam, who both spent decades in prison, are expected to have their murder convictions tossed on Thursday, a bombshell development that will be a boon for critics who have for years expressed doubts over what they believed was a botched investigation.

Many of those critics, who mourned the loss of Malcolm X, questioned whether a double disservice had been done when the men accused of murdering him were put behind bars in what they feared was a discriminatory rush to judgment.

The new investigation was carried out by the Manhattan district attorney’s office, the Innocence Project, and the office of civil rights lawyer David Shanies. Their findings revealed that the FBI and New York Police Department withheld evidence that likely would have yielded the acquittal of both men.

Manhattan District Attorney Cy Vance announced the news in an interview with The New York Times. “These men did not get the justice that they deserved,” he said, apologizing for errors that landed the two men behind bars for decades.

Innocence Project co-founder Barry Scheck said in a statement that the influential civil rights leader’s assassination was deprived of the “scrupulous investigation and prosecution” that it deserved, suggesting that the initial probe “produced one of the most blatant miscarriages of justice that I have ever seen.”

Aziz and Islam, previously known as Norman 3X Butler and Thomas 15X Johnson, were released from prison in 1985 and 1987 respectively. Islam died in 2009.

Efforts to unearth the truth in the decades-old murder case were complicated by the length of time that had passed, and the loss of documents and articles of evidence that could be tested.

Many of the case’s key players—including witnesses, lawyers, and other key suspects—died long before the probe got underway.

Investigators did, however, manage to interview a living witness who goes by J.M., who corroborated Aziz’s alibi. The interview bolstered the claim that Aziz had been at home caring for his wounded legs on Feb. 21, 1965, when three men opened fire in the crowded Audubon Ballroom, killing Malcolm X as he delivered a speech.

A stash of FBI documents cited in the probe also revealed key information that pointed at other possible suspects. And prosecutors’ notes said that undercover officers had been in the ballroom at the time of the shooting, which had not been disclosed, the Times reported.

But the probe did not point to a particular suspect or suggest a government conspiracy to kill Malcolm X. It also didn’t answer lingering questions about who knew of the assassination plot in advance and why it was not thwarted by police or the government.

The probe uncovered police records that revealed a reporter for the New York Daily News had been alerted in a call that Malcolm X would be killed.

In a statement Wednesday, Shanies called the development both “significant and long overdue,” highlighting the tragic fact that Islam died years before having the chance to clear his name.

“These innocent men experienced the agony of decades in prison for a crime they did not commit,” he said. “They were robbed of their freedom in the prime of their lives and branded the killers of a towering civil rights leader.”

“The tragic and unjust events of the past can never be erased but exonerating these men is a righteous and well-deserved affirmation of their true character,” he added.

The Daily Beast has contacted two of Malcolm X’s children for comment on the news.