African National Congress (ANC) President Jacob Zuma's innocence or guilt should be decided by the courts and not through rhetorical statements from his detractors or supporters, retired chief justice Arthur Chaskalson and one of SA's top lawyers, George Bizos said on Saturday.

In an unusual step in the legal world, they issued a signed statement to Sapa news agency saying: "We are concerned at the tone of the debate around the contemplated trial of Mr Jacob Zuma."

Chaskalson and Bizos emphasised they did not want to say anything about whether Zuma should have been charged, or the substance or lack of substance of the charges against him... "those are matters beyond our knowledge".

They were concerned with only one issue, "and that is the implication from some of the statements that have been made that our judiciary as a whole lacks the independence and integrity to ensure that Mr Zuma will receive a fair trial".

This was harmful to the judicial process, South Africa's constitutional democracy and the country's reputation.

Chaskalson and Bizos appealed to all political leaders and their supporters, opinion makers, commentators and the media to let the courts decide on these issues.

"We are confident they will do so without fair or favour."

The pair said an example of where the integrity of the judiciary was called into question was when a Congress of SA Trade Unions (Cosatu) spokesperson reportedly said: "It does not matter who the judge is, we do not believe the judiciary will be able to be objective.

"The trial against Zuma is a politically motivated exercise... and he has been subjected to trial by public opinion for the past seven years.

"We have been convinced for some time that he will not get a fair trial... workers will not allow the NPA [National Prosecuting Authority] and whoever is handling them to abuse its power in this matter."

Cosatu spokesperson Patrick Craven on Saturday denied that the union federation was questioning the independence of the judiciary.

"On the contrary we are defending the independence of the judiciary against what we perceive are attempts to manipulate them by people outside for political ends," he told Sapa.

"The statements made has nothing to do with the court procedures itself but the way it is being handled through public domains."

Craven said Cosatu was trying to protect the judiciary from "the people abusing legal processes for political ends".

"People outside the judicial system are manipulating it for political ends.

"Cosatu are helping to defend the country's constitution," he said.

Bizos and Chaskalson said: "Guilt or innocence cannot be established by rhetorical statements. The question whether Mr Zuma is guilty or innocent must be decided by the courts and not by his detractors or his supporters; so too, the question whether or not he gets a fair trial is a matter for the judiciary.

"Putting pressure on the courts by making serious allegations of partiality, uttering threats of massive demonstrations, and expressing opinions in intemperate language are harmful to the judicial process, to our constitutional democracy, and to our country's reputation.

"We appeal to all political leaders and their supporters, opinion makers, commentators and the media, to let the courts decide on these issues. We are confident that they will do so without fear or favour. That is their constitutional duty and there is no reason to believe that it will not be discharged."

Chaskalson was Chief Justice of the Constitutional Court from 2001 to 2005 and the president of the same court from 1994 to 2001.

During his career he appeared as counsel for members of the liberation movements in several major political trials - including the Rivonia Treason Trial, which led to the conviction and imprisonment of Nelson Mandela and other leaders of the African National Congress. He was also a consultant to the ANC on constitutional issues.

Bizos was appointed by former President Nelson Mandela to the Judicial Services Commission in order to recommend candidates for Judicial office and reforms to the Judicial System to erase its apartheid past. He was again appointed by President Mbeki.

Bizos was counsel to Nelson Mandela since the mid-fifties and was part of the team defending Mandela, Walter Sisulu, Govan Mbeki and others in the Rivonia Trial.

He was an advisor in the drawing up of the Interim Constitution as well as the Bill of Rights.

He also played in role in the Truth and Reconciliation Commission hearings.

With acknowledgements to Sapa and Cape Argus.