Sergeant Marais was 23 and Sergeant van der Vyfer, whose widow is two months pregnant, was 28.
Five other policemen, all of them armed and on duty, were murdered over the weekend in the Johannesburg area. Nationwide, 148 police officers have been killed since January.
Sydney Mufamadi, the Minister of Safety and Security, described the latest spate of police murders as a 'national tragedy'. Mr Mufamadi, who was detained repeatedly by the police during the Eighties for his political activities on behalf of the African National Congress, said he was concerned at the damage being done to South Africa's image abroad at a time when the government was battling to attract foreign investment. 'This is creating the impression of a totally lawless society,' he said.
Crime, including police murders, dropped off abruptly in April and May, the period immediately before and after South Africa's first democratic elections. But in June any hope that political liberation might encourage the country's criminal minds to explore more innocent pursuits evaporated. The official statistics for the PWV (Pretoria-Witwatersrand-Vereeniging) province, which includes Pretoria and Johannesburg, showed that during the month one robbery was committed every eight minutes, 1,044 cars were hijacked at gun- or knife-point, 50 people were murdered in their homes and 10 policemen were killed in the line of duty.
South African criminal experts said this week that when the total number of murders for 1994 came to be tallied it was unlikely the figure would fall below the annual average of 20,000 for the years since 1990.
Jessie Duarte, a former personal assistant to Nelson Mandela, who is now Minister of Police in the PWV government, said on Tuesday measures would have to be taken to ensure criminal elements did not create 'an unseen dictatorship'. One of the new measures, she said, would involve setting up regular police roadblocks all over the province. 'Our gloves are off,' Ms Duarte declared.
Such is the fear assailing the police force, however, that some are admitting they have lost all stomach for the fight. 'It's so dangerous out there that I for one would be afraid to go out and work the streets,' said a police spokesman, Colonel Ruben Bloomberg.
Explaining the rise in police murders in terms of the easy availability of firearms, Colonel Bloomberg said: 'We thought things would get better in the new South Africa but they are getting worse. There was a perception in the past that many attacks on police were politically motivated but this is no longer the case.'
There was also a perception in the past that many attacks by the police were politically motivated.
A case in point was provided yesterday in a Pretoria court, where a former police colonel, Eugene de Kock, charged with numerous murders, appeared before a magistrate in an attempt to obtain bail. The court heard that the state was pressing charges against him in connection with the murder of three policemen - all potential witnesses against him - and the distribution of weapons to members of the Inkatha Freedom Party for 'terrorist' purposes.
The charge sheet against Colonel de Kock, a key figure in the 'Third Force' which orchestrated the township wars of recent years, also included the attempted murder of a former police captain, Dirk Coetzee. Captain Coetzee was an associate of Colonel de Kock's in a police hit-squad during the mid-Eighties. In 1989 he confessed all to the press, fled the country and joined the ANC in London, where Colonel de Kock allegedly plotted to have him killed two years ago.
In perhaps the most dramatic measure of how the politics of the South African police have changed in the 86 days since Mr Mandela became President, the Johannesburg press reported this week that the reinstatement of Captain Coetzee into a senior position on the force was expected soon.