Online videos have long offered extremist recruiters a way to inspire angry and lost young men, to shape them for a battle against Jews, the West, or both. They often confuse Jews with the unpopular policies of the government of Israel, but so do many people in France, Spain, and many other countries in Europe. Some 45 percent of French people surveyed believe that French Jews are more loyal to Israel than to France. In Spain, 72 percent believe the same, according to a survey by the Anti-Defamation League.

Anti-Semitism is a particularly sensitive topic in France — it took until 1995 for a French leader, the incoming President Jacques Chirac, to acknowledge France’s responsibility for deporting 76,000 Jews, in many cases, to their deaths during World War II. “These dark hours forever sully our history and are an insult to our past and our traditions,” Chirac said 53 years after the first mass arrests of Jews in Paris. “Yes, the criminal folly of the occupiers was seconded by the French, by the French state.” To this day, many French Jews remain suspicious of their government’s commitment to protecting them.

In the six weeks after the conclusion of Merah’s rampage, there was a doubling of anti-Semitic incidents (compared to that same period the previous year). A Jewish security watchdog known as SPCJ says that anti-Semitic acts leaped by 45 percent in the first eight months of 2012, and that Merah’s actions have inspired others. In one notable attack near the Beth Menahem Jewish school in Villeurbanne in southern France, a dozen or so men attacked a trio of young Jewish men in yarmulkes on June 2, first insulting and shoving them around, and then beating them with an iron rod and a hammer, sending them to the hospital.

There has been other violence, too, including the strange midday attack on a kosher market in the Parisian suburb of Sarcelles on Sept. 19, days before Yom Kippur. In that attack, two masked men dressed in black entered the store and detonated a weak grenade that shattered the front window of the shop, wounding a bystander who suffered an arm contusion. Sarcelles, a commune of 60,000 people north of Paris, is sometimes referred as Little Jerusalem because of its sizable Jewish community, made up largely of Jews who left North Africa in the 1960s.

Police recovered the pin of that grenade and found the DNA of Jrmie Louis-Sidney, who anti-terror authorities have said they first became aware of in the spring. A 33-year-old father of five children, Louis-Sidney was a resident of Cannes in southern France, but he often stayed with the mothers of his different children or friends outside of Paris or in Strasbourg. The son of Christians, Louis-Sidney — who was known to many people as “James” — did a stint in prison on a drug trafficking conviction where, some family members told French media, that he turned to radical Islam. He eventually grew a long beard. His conspiratorial post-incarceration worldview is on display in a 2009 excerpt of a hardcore rap video he recorded for a song titled, “21e sicle” (21st Century). “September 11 is just the tip of the iceberg,” he declares in a rap that mentions trafficking kids and body organs. He goes on to warn viewers: “Know that you are manipulated. If you don’t understand, inform yourself, prepare yourself, arm yourself with knowledge. Now it is up to you to see.” He ends with the words “Allah Akbar.”