Authorities suspect the same killer was behind attacks last week on French paratroopers of North African and French Caribbean origin.
France was reeling Tuesday after Monday's shooting in the southern city of Toulouse, the deadliest school shooting in the country and the bloodiest attack on Jewish targets in decades. Schools across the country held a moment of silence to honor the victims, who were heading to Israel for burial.
"The children are exactly like you," President Nicolas Sarkozy told junior high children in Paris after joining them for the moment of silence. "That could have happened here."
He vowed to find the killer.
He was speaking at a public school across the street from a memorial to the French people who helped Jews during the Holocaust, when most of France was occupied by the Nazis.
Interior Minister Claude Gueant said the attacker was "wearing around his neck an apparatus" that could be used to film and post video online. He said that gave investigators new clues to the killer's "profile," though he admitted they don't appear to close to an arrest.
Gueant described the suspect as "someone very cold, very determined, very much a master of his movements, and by consequence, very cruel."
In Monday's shooting, the attacker first gunned down a rabbi and his 4-year-old and 5-year-old sons, then chased down the 7-year-old daughter of the school principal, shooting her dead at point-blank range.
Asked whether the gunman recorded the scene, Gueant responded, "We can imagine that." But he added that authorities have not yet found any images of the killings online.
Gueant said authorities are studying reports about three paratroopers kicked out of a regiment near Toulouse in 2008 for suspected neo-Nazi activity, but said is one of many leads and "not favored any more than the others."
He stressed the need to increase security at synagogues and other Jewish sites in France.
"All believers in France must feel protected in their faith," he said.
Sarkozy is meeting with members of France's Jewish and Muslim community. France has the largest population of Jews and Muslims in western Europe.
Hundreds of police are looking for the killer, the terror threat level was raised to scarlet across a swath of southern France - the highest level since the four-point system was created in 2003.
It was the third motorbike killing in the region in about a week. In all three killings, the assailant fled on a motorbike.
In Toulouse on Tuesday, France's fourth city, the town center is usually bustling with activity, but the streets were emptier than normal. In one of the main squares, Place Wilson, a dozen police officers were on patrol, with some guarding the subway entrance.
The shootings echoed across a nation that has been focused on an upcoming presidential race in which issues about religious minorities and race have gained prominence. Sarkozy - who has struck a nationalist line in his campaigning - raised the terrorism alert level in the region to its highest level, while also noting a possible racist motive.
All of the dead were dual Israeli-French citizens.
Police bearing automatic weapons stood in front of Jewish schools in Paris on Tuesday.
"It's impossible not to imagine the worst, because it can happen to any child in France at some point," said Mendy Sarfati, a father dropping his three children off at a Jewish school in Paris. "We wish to put this drama behind us and that the French Republic will draw lessons from it."