Eric Alexander Taylor, a former police lieutenant, was testifying before the amnesty committee of the Truth and Reconciliation Commission in Port Elizabeth. He has confessed to the murders.
He said the four activists were killed because they were seen as a threat to the country.
Taylor said he was having difficulty remembering the leadership structures of the UDF and its affiliates in the Eastern Cape.
He is applying for amnesty for the murder in June 1985 of UDF members Matthew Goniwe, Sparrow Mkonto, Fort Calata and Sicelo Mhlauli.
The committee has heard from two other officers applying for amnesty - Nic Janse van Rensburg and Johan van Zyl - that the Cradock Four were eliminated because they were causing anarchy in the province.
Asked by George Bizos SC, for the families of the victims, to name the executive members of the UDF in Port Elizabeth and Cradock at the time, Taylor was largely unable to do so.
He explained that at the time he knew most of the UDF activists and the positions they held, but had since forgotten who many of them were.
Taylor, who was responsible for monitoring activists in the Cradock area, also had difficulty in describing the positions held by Goniwe, Calata and Mkonto in the Cradock Residents Association, which the police also saw as a threat to security in the area.
Taylor earlier told the committee he still did not know who authorised the killing of the Cradock Four. He said he was led to believe at the time that the order came from "higher up". He says he does not know who made the decision.
"I would still like to know where this line of command stopped," he told the committee.
Taylor said he was convinced until recently that he and other members of the death squad had got away with their crime.
He told the committee it had always been the intention of the squad members to avoid being linked to the murders. Even when the inquest into the death of the Cradock Four was reopened in 1993 he was not worried about being identified.
"If they had not succeeded in solving the case in eight years it was unlikely they would ever do so. Even the (police) murder and robbery unit, who are very efficient, could not solve the case," he said.
Taylor said he began undergoing a transformation in the early 1990s as a result of the release of Nelson Mandela and the start of negotiations on the future of South Africa.
He said that as a result of this process he decided to meet the families of the people he killed, and to apply for amnesty.
He said there was a "heaven's breadth" between his attitude now and what he felt in 1985.
"If we had known in 1985 there would be negotiations in five years' time (1990) we would never have acted that way," he said.
He said the meeting he had with the families of the victims in April last year had been a difficult and emotional experience.
Johann Martin van Zyl and Gerhardus Lotz were allegedly members of the squad with Taylor that killed the Cradock Four.
Policemen Nicholas Janse van Rensburg, Hermanus Barend du Plessis and Harold Snyman have also applied for amnesty for planning the murder.
Convicted killer Eugene de Kock has applied for amnesty for trying to cover up the involvement of the police.
Taylor is expected to face further cross-examination by Bizos on Wednesday.