After he was taken prisoner on the Herzegovina front in May 1992, Deretic was taken to the Lora military prison in Split where he said he had been subjected to various forms of maltreatment.
At the start of the hearing Deretic recognised the four present accused as persons who had maltreated him during his detention in Lora.
The witness said that the defendants, former Croatian military officers, had beaten a civilian, Gojko Bulovic, to death as alleged in the indictment. He said he had seen through the window of his cell when Bulovic was ill-treated.
The incident took place after another civilian, Nenad Knezevic, failed in his attempt to escape and died as a result of gunshot wounds and beating.
Deretic said he had heard about Knezevic's fate from another inmate, Vladimir Zarkovic, who was scheduled to testify on Thursday.