An apartheid-era assassin known as “Prime Evil” for his role in the torture and murder of dozens of black activists is to be set free by the South African government after 20 years behind bars.

Eugene de Kock is said to have been directly responsible for more atrocities than any other individual in defence of white minority rule. He was head of a death squad at Vlakplaas, a farm 15 miles (24km) west of Pretoria, where victims were tortured in gruesome fashion and murdered before their bodies were burned or blown up to destroy evidence. De Kock was sentenced in 1996 to two life sentences plus 212 years for crimes including murder, kidnapping and fraud.

Justice minister Michael Masutha said on Friday De Kock would be released on parole “in the interests of nation-building and reconciliation” and because he had expressed remorse over his crimes and helped authorities recover the remains of some of his victims.

The date of the 66-year-old’s discharge from a high security prison in Pretoria would be kept secret, Masutha added. “However, I need to remind all of us that parole does not reduce the sentence imposed by the court,” he said, pointing out that De Kock could return to jail if he failed to comply with conditions.

The decision to grant parole to a man often seen as the personification of apartheid brutality, reignited debate over the delicate balance between justice and forgiveness in South Africa. Among those killed by De Kock was Winnie Madikizela-Mandela’s former driver. She has vehemently opposed De Kock’s release. But relatives of several other victims have visited him in jail and indicated support for his parole.

Dumisa Ntsebeza, a lawyer frequently targeted for assassination by De Kock and whose cousin was killed on his orders in 1985, said: “What do I think about his release? This is a rule of law question. If a person has met the criteria, he should be granted parole and apparently he has met the criteria and is free to go. There are many people who did the same things he did and nonetheless are walking the streets of South Africa free. Those people have never suffered in the way De Kock did.”

Ntsebeza sat on the Truth and Reconciliation Commission, set up in 1995 to consider amnesty for those who confessed their crimes during apartheid. He added: “There are as many feelings towards De Kock as there are people, but the majority of people I’ve heard speak on this issue appear to have a similar view to mine.”

Sandra Mama, widow of Glenack Mama, who was killed in 1992, also backed the government’s decision. “I think it will actually close a chapter in our history because we’ve come a long way, and I think his release will just once again help with the reconciliation process because there’s still a lot of things that we need to do as a country,” she told the BBC.

Ben Turok, a veteran of the anti-apartheid struggle and a former African National Congress (ANC) MP, noted that former president Nelson Mandela – whose clan name was Madiba – spent longer behind bars. “I can’t help thinking about Madiba’s 27 years and everything that happens now has to some extent be seen in the context of what happened to Madiba,” he told eNews Channel Africa.

“But nevertheless, we want to build a humane society and, personally, I’m pleased that De Kock has been given parole. I think it’s a good thing and he has shown remorse, he has cooperated, and even though his crimes are beyond imagination we want to build a decent society.”

After his arrest in 1994 – the year Mandela came to power – De Kock, a highly decorated former colonel, confessed to more than 100 acts of murder, torture and fraud. He was granted amnesty for most offences – including the 1982 bombing of the ANC’s London offices – but was jailed for six murders found to have lacked direct political motivation.

In a 2007 radio interview, he accused Frederik Willem de Klerk, the last white president, of having hands “soaked in blood” for ordering political killings. De Klerk, who won the Nobel Peace prize jointly with Mandela, has denied the allegations.

Supporters of De Kock’s parole application say he has written letters begging forgiveness, named top officials who gave him orders and engaged with the families of those killed. In 2012, he met Marcia Khoza, the daughter of ANC activist Portia Shabangu, whom De Kock executed after an ambush in Swaziland in 1989. She said after the meeting: “We greeted each other and shook hands. His handshake was firm.”

During the meeting, De Kock described how he shot Khoza’s mother twice in the head before pushing the vehicle in which she was travelling down a slope. She added: “I thought I would cry but strangely enough had the courage to continue to listen to him. I was not jolted because I had long forgiven him.”

Some, including Madikizela-Mandela, have found De Kock’s crimes too heinous to forgive, but others have contended that he was made a scapegoat for many other defenders of apartheid who went unpunished.

When his application for parole was denied last year, De Kock argued: “I am the only member of the South African police service that is serving a sentence for crimes which I had committed, as part of the National party’s attempt to uphold apartheid and fight the liberation movements.

“Not one of the previous generals, or ministers, who were in cabinet up to 1990 have been prosecuted at all.”

Masutha denied medical parole to Clive Derby-Lewis, a far-right politician who masterminded the 1993 assassination of Communist party leader Chris Hani in an attempt to trigger a race war. Derby-Lewis, 78, is reported to be dying of cancer.

James Selfe, shadow minister of correctional services for the opposition Democratic Alliance, said: “If medical practitioners are of the opinion that Clive Derby-Lewis’s illness [stage three lung cancer] is serious enough to warrant medical parole, the minister, not being a medical practitioner, is not in the position to comment on whether Derby-Lewis is incapacitated or not.

“A process was set in place, the minister must respect it. In the case of Eugene de Kock, due process was followed in considering his parole and it was correctly granted.”

Madikizela-Mandela’s spokeswoman did not respond to requests for comment on Friday.