In the early morning of March 11, 2004, four commuter trains were converging on the Atocha train station in downtown Madrid, laded with commuters heading for work. Almost simultaneously, a series of 10 bombs were detonated, tearing carriages apart, killing 191 people and injuring hundreds more. It was the worst terrorist attack ever unleashed on European soil.

It was also the genesis of "War Without Borders," the story the fifth estate eventually produced about the threat and rise of salafist jihadist terrorism in Europe. Veteran fifth estate producer Neil Docherty pitched the idea about what this calamity signified, and whether it meant that Europe had become a focus of al-Qaeda’s attentions.

Docherty also elicited the involvement of the celebrated PBS documentary program Frontline and The New York Times into the project. The fifth estate often does co-productions with Frontline, whereby our staff research, shoot and edit a story while PBS foots much of the bill, with the story airing both on the CBC and on PBS. Moreover, by bringing in The New York Times, we could tap into their vast journalistic pool (at least that was the hope, although in the end the bulk of the research was carried out by the CBC and the freelance stringers we hired).

Docherty also brought on board his friend Lowell Bergman, the American investigative journalist and producer (of The Insider and 60 Minutes fame), and who currently works for the Times. Bergman has good contacts in the U.S. intelligence and counter-terrorism fields. Soon, an arrangement was hammered out whereby we would edit two versions of the story – one fronted by fifth estate host Linden Macintyre, the other by Bergman. The upshot of all this was that the CBC was able to access both money and resources that would have been too expensive to afford on its own – a necessity given the reality we were shooting a story on a distant continent involving many different languages and time-zone considerations.

I was assigned as the associate producer to the story and was soon joined by a good-humored and able journalist at The New York Times’ television division, Michael Schreiber. He and I spearheaded the researching of the documentary.

Our first goal was to learn as much as possible about the Madrid attack. We quickly hired the services of a wonderful and veteran Spanish journalist, Eva Orue, to find out more about the investigation that the Spanish government was conducting into the incident. Eva was the first of about 10 stringers we used in one form or another on this story – all of whom proved essential.

I also began to build a data bank of experts, and of background information on the history of salafist jihadist terrorism in Europe.

One of the first problems Docherty faced was how to talk about a subject that involved six or seven countries without the story seeming to be a repetitive travelogue. We realized it would make the story more palatable to viewers if they had one character to focus on. This problem was solved when police in Milan arrested an Egyptian man touted as the possible mastermind of the Madrid plot. His name was Rabei Osman el Sayed Ahmed. We soon focused our energies on finding out as much as possible about him. The Italian police caught him confessing on wiretaps to planning the Madrid attack. We spent months building a profile of his movements across Europe, as he traveled from Germany to Spain, France, and then onto Italy.

To this end, I flew to Europe last summer to conduct research in person. In Milan, with assistance from a Canadian-born stringer who works for The New York Times, Elisabetta Poveledo, I managed to find out more details of what Ahmed was doing during his time in Milan, including interviewing one of his roommates. I also managed to obtain a pile of court documents that both traced the history of the al-Qaeda cell in Italy, and included the transcripts of the wiretaps the police had conducted on Ahmed during his stay in Milan.

These transcripts were critical in making it possible for us to reconstruct some of his more alarming statements and confessions for the documentary. Over the next few months, we went to great lengths to obtain some of the actual audio excerpts of the wiretaps – and were close to obtaining them from French authorities before they got cold feet.

A breakthrough in the research occurred when a German-based stringer for the Times managed to find a social worker at a detention centre who knew Ahmed and persuaded him to be interviewed. The stringer also helped land an interview with an outspoken London-based jihadist who led the infamous Finsbury Park mosque, renowned for recruiting and influencing jihadists from across Europe. This interview is one of the most compelling in the story.

Another onerous task was to arrange interviews with many of the top anti-terrorism magistrates and police officials across Europe, including Judge Balthazar Garzon in Spain, Jean Louis Bruguiere in France, and Armando Spataro in Italy, all of whom are high-profile personalities in their respective countries. This involved often weeks of patient negotiation and stroking with the various bureaucracies, although the Italians proved to be the most approachable and eager to help us.

Due to length considerations, one of the coups of our research did not even appear in the fifth estate version of the story. A friend, Mohamed Boudjiennae, a Moroccan-born journalist based in Toronto, was flown to Morocco to see if he could land an interview with the Benyaich family, a famous clan that had three sons who had joined the international jihad: one had even died in Afghanistan fighting the Americans at Tora Bora, while two others were in prison for their terrorist activities. Using great persuasive charm, Boudjiennae managed to convince the family to do an on-camera interview – which appeared in the PBS version of the story.

The most difficult aspect of the story was verifying some of the information we were receiving. It was extremely difficult to know whether what you were getting from the European police and media was true, as they had their own vested interest in publishing distorted information. For example, the Spanish arrest warrants for Ahmed said he had belonged to a terrorist organization in Egypt and received training in bomb making while he was in the Egyptian army.

However, an Egyptian journalist we hired to confirm this information couldn’t find anyone in Egypt who could verify it, while the Spaniards would not reveal their sources. Yet the Egyptians had their own reasons not to verify the information, as it proved embarrassing to them, too. Consequently, we didn’t put this information in our story, and qualified it on our website, indicating that Egyptian authorities denied its veracity.

Bruce Livesey is an associate producer with the fifth estate.