The Court of Justice of the Republic (CJR) announced on August 4th that it was launching an inquiry into Lagarde's role in an arbitration procedure that led to a massive payment to a controversial tycoon in 2008. The CJR investigates suspected wrong-doing by ministers.
The payout from public funds cost a total of €400 million, including a compensation payment of €285 million to Bernard Tapie, a businessman, actor and former Socialist minister who is now a prominent supporter of President Nicolas Sarkozy.
Tapie was also convicted and jailed in 1997 for match-fixing and has a tax fraud conviction.
Described by the website as a "damning report", the nine-page document was compiled by the seven judges on the CJR.
It gives a detailed chronology of the events in the case as well as an analysis of why the judges felt an inquiry was necessary.
"The report includes the suspicion that she acted personally with the sole intention of ensuring a large payout to Tapie," said the website.
The document also criticizes a process that contained "numerous anomalies and irregularities" and says Lagarde appeared to have "given voting instructions to representatives" on a key public body in relation to the payout.
Lagarde took the decision in 2008 when she was France's finance minister, a role she gave up in July when she replaced Dominique Strauss-Kahn as head of the International Monetary Fund.
Such an inquiry can lead to criminal charges which, in this case, would be punishable by up to ten years in prison and a fine of €150,000.
Lagarde has denied any misconduct. Her lawyer, Yves Repiquet, said the case was politically motivated, driven by "suspicion abusively cast on Christine Lagarde by a handful of opposition members of parliament for political ends."
"I have a perfectly clear conscience," Lagarde said in June.