French judges issued the order on Monday, AFP reported.
The charred body of Mireille Knoll, 85, was discovered in her apartment on March 23, 2018.
Paris prosecutors in May said there was enough evidence to order a trial on charges that the murder was aggravated by anti-Semitic hatred.
Yacine Mihoub, 28, a son of Knoll’s neighbor who had known her all his life, and his friend Alex Carrimbacus, 22, were indicted in May. Carrimbacus has a history of psychiatric problems.
Carrimbacus had said during questioning that he and Mihoub targeted Knoll for robbery because she was Jewish, a claim denied by Mihoub. Both men have pleaded not guilty.
Knoll, who escaped deportation to a Nazi death camp when French police rounded up Jews in Paris in 1942, was stabbed 11 times before her apartment was set ablaze by the perpetrators.
“As I’ve always maintained, Madame Knoll was killed both because she was an old person unable to defend herself, and because she inspired a particular hate because of her Jewish origins,” Gilles-William Goldnadel, a lawyer for the Knoll family, told AFP.
Lawyers for Mihoub told AFP that the judges “were unable to resist the pressure of public opinion.” He also said that “except for the statements by Alexandre Carrimbacus, nothing justifies an anti-Semitic motive in this case.”