It's a case with two prime suspects. Yesterday's London bombings, according to experts, are either the work of North African-based terrorists accused of Europe's most recent terrorist plots, or British teens shaped into combative ideologues by religious zealots.

Most experts agree the attack on London was likely the work of Islamic terrorists, but there's much less accord about exactly what kind of extremist carried out the attack. Was it the type of terrorist accused of the attacks like the Madrid bombings of 2004, or young, British Muslims who look innocent but are in fact falling under the influence of fanatical clerics?

So far, the only group taking credit for the subway and bus bombs is a mysterious and anonymous group that posted a message on the Internet calling itself the "Secret Organization of al-Qaeda in Europe." But analysts say no terrorist cell that wants to go uncaptured would advertise and use a brand name, much less a name that includes the word "secret."

Besides, al-Qaeda isn't a standard organization, but a term used to describe a set of independent franchises, says Martin Rudner, a terrorism expert at Carleton University. The London bombings were likely the work of one of those franchises, operating freely and not traceable to a central commander such as Osama bin Laden, says Mr. Rudner.

So that leaves the question: What type of franchise: Old or young? Foreign or home-bred?

Mahan Abedin, the editor of Britain's Terrorism Monitor, said it's too early to speculate, but he's leaning toward the usual suspects. "Almost everything that's been happening in Europe in terms of Islamic terrorism has been tied to North Africans," Mr. Abedin said yesterday from Oxford, England. "North Algerians have been active here since the 1990s."

Of the more than 16 people jailed for the 2004 train bombing in Madrid, almost all of them are Moroccan. Again, it's Moroccans and Algerians who make up the more than 30 suspects detained in an Islamist plot to blow up the Spanish High Court. In April 2004, it was a group of 13 Moroccans who were arrested in Paris, accused of plotting the deadly terrorist attacks in Casablanca.

To explain the trend, analysts point to lax immigration policies, poverty and intense recruitment in Europe's prisons, which are disproportionately populated with North-African inmates. It's so bad that in the fall, European Union counter-terrorism chief Gijs de Vries reached out to Algeria and Morocco, publicly saying that Europe needed to form a dialogue with both countries to thwart future terrorist attacks.

But not everyone looks to North Africa for the answer. Lorenzo Vidino [of the Investigative Projec on Terrorism], a Washington academic who made a presentation on terrorism in Europe to the U.S. House Committee on International Relations just three months ago, suggests the London plotters might come from closer to home.

More and more young, middle-class British Muslims are being shaped by the words of extremist clerics, he says. It's that type of fanaticism that's supposed to have inspired an alleged, foiled British bomb plot -- the plot that, police say, involved Ottawa software developer Momin Khawaja.

Mr. Khawaja, the first person charged under Canada's new anti-terror laws, is accused of showing a group of Britons how to detonate bombs using cellphones. Police seized 600 kilograms of ammonium nitrate and arrested nine people in London. Mr. Khawaja was arrested in March 2004 and is currently in jail awaiting trial. None of the charges against him have been proven in court.

The accused ringleader in Mr. Khawaja's case is England's Omar Khyam, the 23-year-old captain of his cricket team, who fits the look of Mr. Vidino's new wave of terror. "They look completely assimilated," Mr. Vidino says. "One of them goes back to Pakistan pretending to visit his family -- goes to a training camp, learns how to make bombs, goes back, becomes the leader of his group of five or six childhood friends."

Many young European Muslims, and some from North America, were involved in a group called Al-Muhajiroun, a political and religious movement that recently disbanded. Al-Muhajiroun, which has been connected to Mr. Khyam and the other accused, was led by Sheik Omar Bakri, an outspoken zealot based in Britain.

In an interview with the CBC a few months ago, Sheik Bakri said he wished he was a member of al-Qaeda. "It's an honour for people today from the Muslim camp to be with al-Qaeda because al-Qaeda is not a group. The problem people don't understand -- al-Qaeda is not a group, al-Qaeda is a phenomenon."

The young disciples of these influential leaders can slip under the antiterrorism radar, Mr. Vidino says. Training camps and men with automatic weapons are clear evidence of a possible terrorist sect. But how is a spy supposed to infiltrate kids at the arcade or twentysomething professionals?

"You really need the help of the Muslim community there," he said. "And then it's fighting the ideology, which is the solution to the entire conflict."

But Mr. Abedin isn't convinced that yesterday's dead and injured are the victims of young extremists. Sheik Bakri's antics are too public -- he's done a whack of interviews with the mainstream press -- and he likes to draw too much attention to himself.

"Terrorism is very much an underground activity, where as these guys are very much overground," he said.

"Any self-respecting terrorist would stay away from these people."