“I’ve absolutely no doubt that Mehdi Nemmouche, who is here now, was my jailer and torturer in Syria. I knew him as Abou Omar,” said Nicolas Hénin.
Ex-captive Didier François agreed.
The defendant, 33, denies murdering an Israeli couple, a local worker and a French volunteer at the museum.
He allegedly travelled to Syria in January 2013 and faces a separate trial in France for his alleged role as an Islamic State jailer.
What the witnesses said
The trial began last month, but it heard for the first time on Thursday from Nicolas Hénin and Didier François, who were held by IS militants in a hospital in Aleppo in June 2013 and freed in April 2014, a month before the Jewish Museum attack.
Of the 23 foreign hostages held by IS, eight were in Aleppo, and Mr François told the court that their captors were all part of a structure, and were involved in organising the Paris and Brussels bombings in November 2015 and March 2016.
He said Paris bomb-maker and Brussels airport suicide bomber Najim Laachraoui was one of the guards.