PARIS, France (CNN) — It began with a chance encounter last October, outside a courtroom at the Palais de Justice in Paris. Now, Mohamed Sifaoui is under 24-hour protection, getting death threats daily.
Sifaoui, an Algerian-born journalist living in France, was covering the trial of Islamic militants accused of carrying out a bombing campaign in France in 1995.
Also watching the trial was a heavy-set man named Karim Bourti, convicted in 1998 of terrorist association, who has served his sentence.
"Karim recognized me and realized we had gone to high school together in Algeria," said Sifaoui.
That chance meeting led to a three-month journey. In the company of Bourti, Sifaoui — using an assumed name — penetrated the ranks of Islamic extremists in France and Britain — some linked to al Qaeda.
"Every day there was tension. I worked under terrible pressure. I was afraid that at any moment, I might come face to face with someone who knew me, who knew my real name," said Sifaoui.
Bourti and his friends knew Sifaoui was a journalist, even knew he was working on a documentary for the television channel France 2, but they became convinced he was a believer just like them.
"I constructed a new identity. It wasn’t me, I’m anti-fascist and anti-extremist, but it was someone who was sympathetic to them," said Sifaoui.
Sometimes Sifaoui would openly tape interviews with them, other times he used a hidden camera. All the time he was compiling material not only for the documentary, but also for a book.
Sifaoui stayed with his new friends, in the immigrant neighborhoods that ring Paris, watching as they raised money on the streets. He prayed with them at mosques and listened to their political and religious arguments.
Sifaoui said he learned they were recruiting young men to go off to fight jihad, holy war, in Chechnya.
"When there is war, they incite, they encourage young people who don’t have a great deal of knowledge, indoctrinate them, incite them, to send them off to battlefronts," he said.
Gilles Leclair, who co-ordinates anti-terrorist actions for the French Interior Ministry, said that what Sifaoui describes matches the findings of police investigations. He called Sifaoui’s book and television work "good reportage."
"They (the militants) try to get these people to become terrorists, or stronger than normal believers. They are recruiting in jails and in mosques," Leclair said.
Sifaoui said he found more evidence connecting Bourti, and the people around him, to what judicial officials say were chemical weapons plots thwarted by arrests in the suburbs of Paris.
"I knew that he knew the people who had been arrested. I became certain that he and his group were not simply people whose role it was to incite … these people were actively involved in acts of terror," Sifaoui said.
He has more undercover footage that he said backs this up, and that will be part of another documentary that airs on the French channel M6 in coming weeks.
Bourti is now under arrest, suspected by French police of involvement in the beating of a Muslim cleric, and of involvement in a terrorist organization.
Sifaoui’s book,(My Brothers the Assassins), published in France, details what he learned in the months he spent getting close to Bourti. Sifaoui said it is being translated into English and will soon be published in the United States.
As a result of the book and the documentary, Sifaoui is getting death threats. Just within the past week, he said, he agreed to police protection.
He must soon decide whether to testify against Bourti and others. He has not forgotten, he said, that the men who called him "brother" were prepared to kill at any price.