The testimony to the Hefer commission of two former ANC guerrillas and "prison graduates" that it was Mr X who betrayed them - and not Bulelani Ngcuka, the national director of public prosecutions - has inevitably triggered speculation on the identity of the traitor in their midst.

The commission has been careful to give as few clues as possible about his identity, even going to the extent of blacking out the name of the person within the ANC with whom Litha Jolobe, the former guerrilla, communicated before he was ensnared. What is known, however, is that Mr X is dead, that members of his family are alive and that he operated in the Natal theatre of the guerrilla war orchestrated by the ANC from Swaziland.

A name whispered in private conversations, although not in formal testimony, is Musizwakhe Ngwenya, a former ANC guerrilla whose nom de guerre was Thami Zulu, or, more simply, TZ, and whose personal profile fits some of the main clues.

He is dead, having died, shortly after being released from detention by the ANC department of security and intelligence in Lusaka in November 1989.

He left South Africa in 1975 to join the ANC, trained as a guerrilla in the Soviet Union and rose to become commander of the Natal machinery, as the ANC referred to its guerrilla operations in Natal, a command he exercised in the main from Swaziland.

ANC security, or Imbokodo, detained him in mid-1988 on suspicion of being an agent of the South African government, in part because of heavy losses suffered by the ANC on the Natal front.

Members of his family, including his father, Philemon Ngwenya, are still alive. Aged 78, his father is determined to fulfil his quest to clear his son's name.

A former Soweto headmaster, Philemon Ngwenya is convinced his son was an innocent victim of Imbokodo's zealotry. He appears unfazed by conjecture that his son might be Mr X.

He remembers how his son kept looking out of the window of his hideout when the Swazi police, then suspected of being in league with the old South African Police (SAP), were hunting for him in the 1980s, insisting it was not the reaction of a man with powerful protectors in the SAP.

His faith in his son's integrity is sustained by a tribute to him signed by Joe Modise, the commander of the ANC guerrilla army, Umkhonto we Sizwe, and Chris Hani, Umkhonto's chief of staff. Ngwenya senior carries it with him. Compiles after his son's death, the tribute praises TZ as an "outstanding strategist", a "gallant warrior" and a man of "remarkable courage" who, in his capacity as commander of the Natal machinery, made Durban the most bombed city in South Africa".

The death of TZ shortly after his release from detention by Imbokodo (the stone that crushes) is not a glorious moment in ANC history.

As the ANC commission of inquiry into his detention and death records in its report : "Once a commander of Umkhonto we Sizwe noted for his proud bearing and authoritative manner, TZ died an emaciated and sad figure in the University hospital in Lusaka, less than a week after being released from confinement by the ANC security."

His father asked, in a prescient memo written in Lusaka during a visit there in July 1989 - in a vain bid to save his son from what he sensed was the danger of impending death : "Is he being destroyed physically, mentally and spiritually?"

He juxtaposed the question with an observation in the same memo : detainees in South Africa who die in detention are deemed to have "committed suicide" or "swallowed poison".

A finding of the ANC commission of inquiry nine months later resonates eerily with Philemon Ngwenya's observation.

The report refers to a biochemical report on TZ that "indicated the presence" of the poison diazinon in his body. For that reason it concludes that the likelihood is that he indeed was poisoned and that a South African government agent was probably responsible.

On the critical issue of whether TZ was an agent of the previous ant-ANC government, the report states : "There was no direct evidence that he was an agent ....On the evidence placed before us by (ANC) security, he was a suspect and no more."

It continues : "He was never charged with being an enemy agent, nor was such a charge pending."

The report adds an important rider : once a suspect is released without being charged, the status quo reverts and he is entitled to the presumption of innocence : "There is nothing in the (ANC) code of conduct that permits persons to be labelled not-cleared."

The clues about Mr X that may be construe a pointing to TZ must, however, be balance against those that point away from him.

There is an important time difference between the events described by witness Jolobe and his co-witness, Ntobela Maqubela, and TZ's assumption of command of the Natal machinery. Jolobe and Maqubela are describing events that occurred in November 1981, whereas TZ was not appointed commander of the Natal machinery until 1983, according to the ANC commissioner of inquiry.

Beyond that, there is a hint in Jolobe's affidavit that Mr X was a political commissioner in the ANC, not a military commander.

There is another factor to consider : TZ had enemies in the ANC, in part because he came from Soweto, not Natal, and was thought therefore to be unsuitable for the position of the commander of the Natal machinery.

Yet another possibly overlapping factor to be taken into account is the excessive zeal of Imbokodo and its excessive inclination to confuse independence of mind and high self-esteem with treachery, and thus to make false accusations against patriots while leaving real traitors undetected.

All of this speaks volumes about the need to exercise restraint and to think again before pointing fingers at putative spies.

The Hefer commission seems to be gearing itself up to subpoena high-ranking officials in the National Intelligence Agency to help it determine whether Ngcuka was a spy or (by implication) the victim of a false accusation.

Perhaps it should ignore the ANC injunction prohibiting Zuma from testifying and invite him to do so : he was, after all the ANC chief of intelligence during the time when Ngcuka is alleged to have worked for the enemy and, later, when TZ was detained on suspicion of being a government agent.

A question posed by Philemon Ngwenya in his 1988 memo still awaits an answer from Zuma : "Is my son a freedom fighter in the movement or a tool of one man who throws away the keys when he goes away?"

Patrick Laurence is the editor of Focus, the journal of the Helen Suzman Foundation.

With acknowledgements to Patrick Laurence and the Sunday Independent.