FIA president Max Mosley says that race fix claims surrounding Renault are being viewed by the governing body as more serious than outright cheating, after revealing on Friday that Nelson Piquet has been granted immunity.
Renault has been called to appear before the FIA's World Motor Sport Council on September 21 to answer charges that it deliberately told Piquet to crash in last year's Singapore Grand Prix to help Fernando Alonso win the race.
Those claims have been denied by the team, which has begun criminal action against Piquet and his father Nelson for alleged blackmail over the suggestions.
Mosley said the FIA had no choice but to launch a proper investigation into the matter after Piquet had informed the governing body of the events, and he made it clear on Friday about how grave he deemed race-fixing to be.
"If you look at any other sport, if somebody fixes the result then it's usually taken seriously," said Mosley, speaking to the media in his office at the Monza circuit. "Fixing is one degree worse than cheating.
"If you're a cyclist and you take dope, that's cheating. If you bribe the other cyclists, or you get somebody to have a crash in the peloton so the yellow jersey guy crashes, that's more serious.
"Then if it puts human life at risk, whether it's the spectators, the marshals or the drivers, then it's more serious again. The moment we talk about that, we sort of imply they (Renault) are guilty, but we don't know. Until they put their defense in, we've got to assume they're innocent."
Mosley said it was too early to make a judgment, as the governing body was still waiting for Renault to provide its defence submissions.
"We originally gave them until [last] Monday to put in all the documents, and then they have asked for more time, which they have been given until the middle of next week. And, we have got no idea what they will produce. But in the nature of things, there are always two sides to a story."
He added: "Well, if, and it is a very big if, they are guilty, obviously it is very serious indeed. But we are in a situation at the moment where we have heard one side of the story and have investigated to the best of our ability.
"Now we are waiting for Renault's side of the story, and it is only when we have got both sides, and both of them have been heard, that one can actually reach a conclusion. So, in most places, you assume someone is innocent until they are proven guilty. And that is the situation we are in at the moment."
Mosley has confirmed that Piquet himself has been promised immunity from being punished over the matter, as part of the deal for him providing evidence.
"We have said to him that, and I don't know exactly how it was phrased, but he has been told that if he tells us the truth then he will not be proceeded against individually," he said. "It is exactly the same as it was for Alonso [in the McLaren case in 2007]."
Mosley has also expressed regret that documents relating to the Renault trial were leaked this week – and says that action will be taken in the future to ensure that it does not happen again.
"That is actually very unfortunate because it is just one side of the story," he said. "We are quite genuinely curious at to how that happened. Next time, when we send out to 20 or 30 people, we will probably arrange it in such a way that we can tell who is leaking stuff.
"We don't know how it happened. But none of that means anything. What means something is when we get their defense, which will not be until next week."
Mosley confirmed that the most severe penalty of total exclusion from the world championship was a possibility if Renault was found guilty, and he clarified that it was now too late for the result of last year's Singapore Grand Prix or World Championship finishing order to be changed.