"The decision is significant in that it is a departure from the inquest findings that nobody was to blame," the family said in a statement issued by his son, Nkosinathquest findings that nobody was to blame," the family said in a statement issued by his son, Nkosinathi.
The family said it was reviewing the findings of the TRC's amnesty committee, and taking legal advice.
"Similarly, we trust that the Attorney-General of the Eastern Cape will decide appropriately," the family said.
The committee on Tuesday dismissed the application by four former Port Elizabeth security policemen for amnesty for Biko's death in custody.
The TRC found that Biko died of a head injury sustained on September 6, 1977, during a scuffle with policemen when his head collided with an object in room 619 in Port Elizabeth's Sanlam Centre. He died six days later in Pretoria Central Prison.
An inquest set up by the apartheid government shortly afterwards found no one responsible for his death.
The TRC committee found that the policemen, Harold Snyman (who has since died), Daniel Petrus Siebert, Jacobus Johannes Oosthuysen Beneke and Rubin Marx, did not qualify for amnesty because their actions in Biko's death could not be associcated with a political objective.
The committee was also not satisfied that the men made a full disclosure of the facts.
"In the pile of half-truths, lies and amnesia that have characterised the inquest as well as the (TRC) hearings, there are a number of certainties," the family said.
Since Biko suffered extensive brain haemorrhaging from injuries that could not have been self-inflicted while in the company of the applicants, one or more of the officers was accountable for his death, said the family.