Former South African President Thabo Mbeki used state prosecutors as a political tool against his then deputy Jacob Zuma, new court documents say.
The National Prosecuting Authority filed the papers to block an opposition attempt to reinstate corruption charges against President Zuma.
The multimillion dollars charges were controversially dropped on the eve of the 2009 elections.
Mr Zuma, who denies any wrongdoing, ultimately won those elections.
He had just won a bitter battle against Mr Mbeki for control of South Africa's governing African National Congress.
Mr Mbeki has always denied interfering in the prosecution of his rival.
At the time the charges were dropped, acting National Director of Public Prosecutions Mokotedi Mpshe said there was "proof enough of a political conspiracy against Zuma" but he did not reveal many details.
The BBC's Milton Nkosi in Johannesburg says we are now seeing some of the alleged evidence.
Analysis: Milton Nkosi, BBC News, Johannesburg
Essentially what's happening here is that the in-fighting which reared its ugly head in 2007 between Thabo Mbeki and Jacob Zuma has come back to haunt both leaders of the ANC.
The opposition Democratic Alliance is trying every possible available legal avenue to reinstate the corruption charges against Jacob Zuma.
Some say the DA lost the contest at last year's elections when it was trounced by Mr Zuma's ANC and now it is making an attempt to dethrone him via the courts.
The ordinary person in the street is left completely dumfounded by all this destructive rivalry, which is diverting attention from the real issues facing the country such as inequality, poverty and unemployment.
In an affidavit, current NPA deputy director Willie Hofmeyr said that Leonard McCarthy, then a top official of the disbanded Scorpions anti-corruption unit, was used as a "proxy" by former national director of public prosecutions Bulelani Ngcuka.
Mr Ngcuka was directing the Zuma prosecution, "and possibly other prosecutions and investigations".
"It was Ngcuka working with others and not McCarthy who ultimately decided to prosecute Zuma," the court papers say.
Mr Hofmeyr's 153-page affidavit said it appeared from the text of their conversations that former minister of intelligence and anti-apartheid struggle activist Ronnie Kasrils "acted as a conduit for McCarthy to communicate with Mbeki without arousing any suspicions".
The main opposition party, the Democratic Alliance (DA), said the dropping of corruption charges against President Zuma was unconstitutional and irrational.
Even after the NPA's latest affidavit, the DA's James Selfe said the charges must be reinstated "without delay".
Mr Mbeki's office respondent with a brief statement saying that the former president is weighing up his options "on an old allegation."