Mohamed Merah, the Frenchman who assassinated three French paratroopers of North African background and then launched a terrible attack on a Jewish school—murdering a teacher, his two young sons and an 8-year-old girl—claimed to act for al Qaeda. Skeptics have dismissed the claim, saying al Qaeda barely functions anymore. But Merah was no "lone wolf" and did indeed bear the imprint of al Qaeda.

Young and alienated, Merah had served two years in a juvenile prison for robbery. Was he rejected by French society because of his Algerian background? "He snapped," say friends. After prison, he was completely cut off from reality, said his lawyer.

In fact, Merah was practically a prince in French jihadist circles. His mother is married to the father of Sabri Essid, a leading member of the Toulouse radical milieu who was captured in Syria in 2006. Essid and another Frenchman were running an al Qaeda safe house in Syria for fighters going to Iraq. In a 2009 trial that came to be known in the press as "Brothers for Iraq," they and six others were convicted in France of conspiracy for terrorist purposes. Essid was sentenced in 2009 to five years imprisonment.

Family contacts could have been instrumental in setting up Merah's jihadist contacts and facilitating his travels to South Asia. Le Monde reports that the Pakistani Taliban and the Uzbek Islamic Movement trained Merah to become a killer. In 2010, he was captured in Afghanistan (reportedly by Afghan forces) and handed over to the French government, yet French media report that he was able to return to Northwest Pakistan in 2011.

The French police have confirmed that Merah was under periodic surveillance in recent months. That he slipped through and was able to carry out his attacks will become a source of criticism and self-recrimination on the part of the generally efficient French police. It certainly suggests that he had help from a network.

In executing his attacks, Merah did everything by the jihadist textbook. He made sure he would die a martyr's death that would be witnessed on television screens around the world. He murdered with a video camera strapped to his body, making him star and director of his own epic. He told journalists his videos would soon be uploaded. In the attack at the Jewish school Monday morning, Merah held a little girl by her hair while he paused to reload his gun. He then shot her. In a recording found in his apartment he tells another victim, a soldier: "You kill my brothers, I kill you." This is theater.

The Internet was his friend. "I have changed my life . . . on video," said one of his last tweets (in French) during the siege. His account ID featured a black knight on a horse holding high the flag of jihad.

He signed that last tweet "Mohamed Merah-Forsane Alizza." Forsane Alizza, or "Knights of Glory," is a France-based jihadist media organization that was banned in January by French authorities after they discovered members preparing to train in armed combat. The ban made little difference, as content was uploaded to new sites. A website using the Forsane Alizza alias is still active—and registered with a domain name registrar and Web hosting company based in the state of Washington.

Two hours before the police arrived at his apartment, Merah was calling a French TV station. He appears to have had the media on speed-dial and was an active user not only of Twitter but of Facebook and YouTube. (Authorities took down his online outlets one-by-one on Wednesday.)

Merah's shootings in Toulouse again shatter the illusion that counterterrorism can be 100% successful. Jihadist terrorism exploits our freedoms and opportunities in a global campaign linking foreign insurgencies and extremist activism in the West. Highly scripted and planned with the assistance of accomplices in and outside of France, Merah did not act in isolation.

Ms. Klausen. a professor of politics at Brandeis University and author of "The Cartoons That Shook the World" (Yale University Press, 2009), is founder of the Western Jihadism Project, which tracks and analyzes the development of jihadi networks in the West.