The Swiss pharmaceutical company Novartis said an internal investigation hasn’t produced any evidence that bribes were paid to 10 Greek politicians who are rivals of the ruling Radical Left SYRIZA, although Prime Minister Alexis Tsipras said they were guilty anyway.

Trailing badly in the polls in an election year, Tsipras said Novartis and his rivals were at the heart of the biggest scandal ever in Greek history but not has been found yet. The case is based on the testimony of three whistleblowers who said they heard somebody saying bribes were paid but their stories have been said to keep changing.

Their identities had been kept secret under whistleblower laws but the name of one was revealed after he was stopped at the international airport in Athens trying to go to Spain. The accused, including two former prime ministers, a former finance minister,, European Union migration chief Dimitris Avramopoulos and Bank of Greece Gov. Yannis Stournaras have denied wrongdoing and some are suing and demanding to know the names of others who said the took bribes.

The firm did not receive preferential pricing from the Greek state and has so far been unable to trace any “inappropriate payments” to government officials, a local spokesperson told Bloomberg in an email exchange, according to the report.