A fifth officer involved in the killing was denied amnesty in December.

The Commission's Amnesty Committee said it made its decision after finding that the men had lied in their testimony about the events leading to Mr Biko's death, and had conspired to conceal the truth about them.

The committee also found that the killing of Mr Biko was not politically motivated, the requirement for granting amnesty.

The denial of amnesty allows Steve Biko's family to bring a civil suit

Steve Biko's family has welcomed the decision.

"He was a man who was arrested healthy and who died of a brain haemorrhage. The courts afterwards found nobody to blame, and its hard to understand why. This is a significant step in putting the history books straight," Steve Biko's son Nkosinathi said.

A lawyer for the family, George Bizos, told the BBC that criminal proceedings against the men had already been submitted to the attorney general of the Eastern Cape, who was now deciding whether to charge them with murder.

Struggle for justice

Steve Biko was one of the leading anti-apartheid figures and the decision means that his family will be able to bring a civil action against the men.

The committee's verdict had been expected after the four officers - Harold Snyman, Daniel Siebert, Jacobus Beneke and Rubin Marx - gave similar testimony to Gideon Nieuwoudt, another officer who was refused amnesty last year.

Officials have said Mr Nieuwoudt is open to criminal prosecution.

The five said Mr Biko tried to attack one of his interrogators while in custody in Port Elizabeth. They said they tackled the 30-year-old anti-apartheid campaigner and accidentally slammed his head against a wall.

Martyr's death

He was then taken in a police van, naked and bleeding, on a 750-mile (1,200-kilometer) trip to a prison in Pretoria, where he died of brain injuries on 12 September 1977.

Steve Biko was a hero among young people in South African townships and his death made him a martyr in the struggle against apartheid.