South Africa's Truth and Reconciliation Commission rejected amnesty for the three surviving officers who interrogated the black consciousness leader in 1977. Another has since died and the fifth was denied amnesty in December.
Any prosecution would be likely to re-inflame passions about a man who became synonymous with resistance to apartheid. The case sparked an outcry at home and abroad and hastened the end of white minority rule.
Les Roberts, top prosecutor for the Eastern Cape province, said in a telephone interview that he would re-open the case.
"We are going to have to make a study of the whole issue. It's quite a complex one, working out whether we have a case to prosecute or not," he said. "All I want to say is, the matter is open."
But his remarks suggested the chances of prosecution were not overwhelming.
The statute of limitations for any count less than murder has expired. Other prosecutors - and Roberts himself - had found there was not enough evidence to prosecute the officers on lesser charges. And the statements made by the officers to the panel would most likely not be admissible.
"Our options are murder or nothing," Roberts said.
The likelihood of a murder charge rests mainly on the hope that one or more of the four officers would turn state's evidence and testify against the others, he said.
Roberts didn't rule out other strategies.
"One never knows. In criminal cases, funny things can happen," he said.
The human rights panel on Tuesday rejected amnesty for policemen Harold Snyman, Daniel Siebert, Jacobus Beneke and Rubin Marx. Snyman died of cancer and Gideon Nieuwoudt's application was considered, and rejected, separately.
The panel denied them amnesty because they had failed the cardinal test - - they admitted no crime. Further, the panel found they had continued their lies of decades about the circumstances of Biko's death.
The five said Biko tried to attack one of his interrogators while in custody, and that he accidentally slammed his head against the wall during a scuffle that ensued.
The panel said they most likely were angered by Biko's defiant posture - including sitting in a chair without permission.
Biko, 30, remained chained naked to a metal gate in a standing position for two days. He was then taken in a police van on a 750-mile (1,200- kilometer) trip to a prison in Pretoria, where he died of brain injuries on Sept. 12, 1977.
"I do believe there has to be a prosecution and it has to happen speedily," said Peter Jones, a friend who was with Biko at the time of the arrest. "I'm looking at a murder trial," Jones told SABC radio.