In his memory (Photo: Reuters)
Jewish and anti-racism groups organizing the main rally in Paris said up to 200,000 people walked through the east of the capital, past the mobile telephone shop where the murdered man, Ilan Halimi, worked.
Police put their number at 33,000. Some lit candles or released white balloons as they passed the shop, while others sang the French national anthem or chanted Jewish prayers.
Police patrolled the crowd in Paris, where an array of ministers, including Interior Minister Nicolas Sarkozy, joined the march. Opposition Socialists, including former Prime Minister Lionel Jospin, as well as members of other parties, were also present.
They made their way from the Place de la Republique to La Place de la Nation, in eastern Paris, in a chilling cold.
"Today, we must march, we must stand up, to say that in France each of us has the right to live in dignity whatever his God, his religion, the color of his skin," said Foreign Minister Philippe Douste-Blazy.
Halimi's abduction and murder has sent shockwaves through the country, and raised tensions between France's large Jewish and Muslim communities.
Halimi, 23, was kidnapped in January by the gang, which, among other tactics, apparently used young women as "bait" to lure men into a trap. He was held for three weeks while his abductors sent ransom demands to his family.
On February 13, Halimi was discovered, naked, bound and gagged, with horrific burns and stab injuries, alongside a railway track near Paris. He died while being taken to hospital.
Tipped off by one of the "sex-bait" women, police quickly swooped on a number of suspects, which has grown to 17 with recent arrests.
The alleged ringleader, identified by prosecutors as Youssef Fofana, 25, was arrested in the Ivory Coast capital Abidjan and France has requested his extradition.
Fofana, a convicted petty criminal of Ivorian origin and with French citizenship, is suspected of being behind two other extortion rackets that involved threatening doctors, businessmen and minor celebrities.
Questioned by police, he allegedly said the gang targeted Halimi because he was presumed as a Jew to be wealthy, but denied being the killer or that he was motivated by anti-Semitism.
Gang leader shows no regret
Police said they had confirmation that four of six other potential kidnap victims tracked by the gang were also Jewish.
"He has shown no remorse, no regret," an investigator said of Fofana, who was expected to be extradited to France this week.
On Saturday, two of the young women accused of acting as sexual bait appeared before a French judge and were placed under formal, criminal investigation as a precursor to being charged as accessories to kidnapping, criminal association and illegal detention.
A male suspect was also placed under investigation.
Although the gang allegedly includes whites, blacks and Arabs, media attention has focused on its Muslim members, stoking animosity between members of France's 500,000-strong Jewish community and the five-million-strong Muslim population.
The Paris demonstration included figures from across the political spectrum, as well as the leaders of rights groups, unions, student bodies, and Jewish and Muslim associations.
Far-right politicians also attempted to participate in the rally, despite protests from organizers and left-wing groups. One, Philippe de Villiers, leader of the Movement for France party, was forcibly expelled by private security guards employed by the organizers.
"I am here to stress the need to stop the racist and anti-Semite acts that led to the death of Ilan," the head of the CRIF French Jewish organisation, Roger Cukierman, told AFP.
"It's important for French society to realize that little anti-Semite and racist prejudices can have terrible consequences."
Silent marches of between 1,000 and 2,000 people took place in the cities of Lyon and Bordeaux, with demonstrators carrying pictures of Halimi and banners reading "Rest in Peace, Ilan".
The French government was wary about drawing too heavy a link between the criminal gang responsible for Halimi's murder and anti-Jewish sentiment, however.
Past incidents in which apparently anti-Semitic crimes turned out to be staged or committed for other motives seemed to lie behind its cautious stance.
A government spokesman, Jean-Fran‡ois Cope, told French radio that while there were "strong suspicions" of anti-Semitic motives in "this horrible affair", investigators were still getting to the bottom of the case.
"Absolutely everything must be done to know all the details" before conclusions about racism or anti-Semitism were drawn, he said.