Judges investigating suspicions that senior politicians, including Nicolas Sarkozy, were implicated in the use of kickbacks from defence deals to illegally fund a presidential campaign have uncovered a dramatic new piece of evidence. The document, published here by Mediapart, shows that as budget minister Sarkozy signed a letter backing the complex set-up that led to the illegal payments. The document, which dates from 1994, contradicts claims from the former president that he had no involvement in the affair. Its discovery coincides with moves to get Sarkozy and two other former ministers investigated by a special court that handles allegations of offences committed by ministers in the line of duty. Fabrice Arfi and Karl Laske report.