Sarkozy allegedly took money from Muammar Gaddafi to finance his Presidential campaign. There's been a rumor for years that French agents killed Gaddafi to prevent him from spilling that and other French secrets if he was ever put on trial. Gaddafi was tortured/maimed by his initial captors, but someone else got to him later and shot him in cold blood.

Another reason the French intervened/killed Gaddafi was Libya wanted to use its considerable oil wealth to challenge the French neocolonial empire in Africa, which controls the financial systems of French ex-colonies. Libyan mercenaries armed/financed by France to overthrow Gaddafi then went on to invade Mali and help topple the government there, allowing French troops to return to the country for the first time since independence.

Sarkozy was also generally corrupt and got caught in a number of less interesting schemes.