C died of poisoning. For this reason, A and B were interrogated by the judge. A said that if it was murder, it must have been done by B. B says that if it's not suicide, it's murder. The judge made the following assumptions: (1) if neither A nor B lied, then it was an accident. (2) if one of A and B lied, then it was not an accident. The final facts show that the judge's assumption is correct.
The statement 'C is suicide' most severely weakens the above argument.