France's half-a-million-plus Jewish community is the largest in Europe but has been hit by a wave of emigrations to Israel in the past two decades, partly due to the emergence of a virulent strain of anti-Semitism in predominantly immigrant neighbourhoods.
Mireille Knoll was stabbed 11 times in her apartment in the 11th arrondissement of Paris before her home was set on fire, according to government spokesman Benjamin Griveaux, who recounted the attack on Twitter.
A French judicial official says two suspects have been given preliminary charges for the murder with anti-Semitic motives of an elderly Jewish woman.
"We are really in shock", says Knoll's son, noting his mother had "no money" to tempt her alleged killers.
"We have understood, with horror, that anti-Semitism is still alive", he told CRIF, an umbrella group of Jewish organisations.
One of the suspects was a long-time neighbor who recently finished a jail sentence for a sex offense, the victim's son Daniel Knoll told i24 News, an Israeli channel.
The French newspaper Le Monde reported that the first suspect is 27 years old, and one of Knoll's neighbors who used to visit her on a regular basis. Authorities on Monday said they were investigating whether her religion was the reason she was killed.
Mireille Knoll was stabbed repeatedly before her attackers set her apartment on fire.
"For the Jews of France, the nightmare continues".
After the war Knoll returned to Paris and married a Holocaust survivor, who died in the early 2000s.
Jewish groups had reacted angrily to the investigators' delay in declaring that killing an anti-Semitic act.
French President Emmanuel Macron tweeted that Knoll's death was a "horrific crime", and reaffirmed his "absolute determination to fight against anti-Semitism".
Jews had become "a particular target" in the terrorist attacks that have hit France in recent years, and were also suffering from "an anti-Semitism that expresses itself with the greatest violence", Kalifat warned.
A Holocaust survivor, Knoll had managed to evade as a child the 1942 Vel d'Hiv Nazi-directed roundup by French police of more than 13,000 Jews who were sent to Nazi death camps. In 2012 Mohamed Merah killed four people, including three children, outside a Jewish school in Toulouse.
France's Jewish community has voiced increasing concern over a rise in violent anti-Semitic acts in the country.
But she adds that there's still "much more that needs to be done" to ensure the safety and security of Jewish people.