The journalists who were freed in April 2014 came to the Belgian capital to testify about the character of Nemmouche, a 33-year-old Frenchman who faces a life sentence if convicted of the murders.
Francois said Nemmouche hit him with "around 40 blows of a truncheon" among other abuses during the time the journalists were held by the Islamic State in the hospital turned prison.
He added that the violence and "tortures" meted out by Nemmouche mainly targeted Syrians and Iraqis also held there.
The four French journalists were kidnapped in June 2013 and held hostage by the IS in the northern city of Aleppo until April 2014.
Nemmouche's lawyers charged that their testimony amounts to a "stunt" and a "trial within a trial" because their kidnapping is the subject of separate proceedings in France.
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