In the days following the fall of the Srebrenica enclave, Ruez left The Hague for Tuzla to investigate allegations regarding the killing of detained Muslim men, which was the start of the investigation that eventually, thanks largely to his skills and perseverance, disclosed to the world the whole scope of the July 1995 crimes. That criminal investigation, arguably Europe’s largest in the 20th century, began by interviewing Srebrenica refugees pouring into Tuzla and ended with genocide and war crimes convictions at the ICTY of Bosnian Serb Army commander Ratko Mladić, political leader Radovan Karadžić, BSA general Radislav Krstić and other BSA officers.
Ruez was a crucial witness at those trials, testifying about the development and findings of his investigation. He also testified before the Investigative Commission of the French National Assembly in 2001.
After six years of intensive work on Srebrenica crimes, Ruez left the ICTY and eventually returned to the French police force in 2003.