MADRID, Spain (CNN) -- Defense attorneys argued Thursday in Madrid that prosecutors have a weak case against 11 suspected Islamic militants charged with plotting suicide attacks on Barcelona's metro last year.
The attacks, prosecutors said, were to be followed by attacks elsewhere in Europe.
"There was no bomb in Barcelona," defense attorney Jacobo Teijelo said on the first day of trial. "The police said there would also be bombs elsewhere in Europe, but there weren't. Not even arrests. Their argument is full of holes."
The attacks never happened. Police arrested the suspects in January 2008 after an informant warned authorities about a plot.
Jose Maria Fuster-Fabra, the private prosecutor representing victims in the case, said there were contradictions in the testimony of four of the defendants on the first day of trial.
Fuster-Fabra added that testimony from the informant, known was witness F1, would be crucial.
"I think the testimony of the protected witness, F1, will be very important, along with the testimony from the Civil Guards who handled the investigation," he said.
The suspects "were preparing and organizing a series of terrorist attacks in Europe that would start in Barcelona," prosecutor Vicente Gonzalez Mota wrote in a document outlining the charges.
Four of the defendants arrived in Barcelona shortly before the planned attacks, at least two of them from Pakistan, the prosecutor said, and the group allegedly was under the influence of Baitullah Mehsud, a Pakistani Taliban leader of the radical Tehrik-e-Tabligh movement.
Mehsud was to make demands after the Barcelona attack, and if the West refused, further attacks in Europe would have followed, the prosecutor wrote.
The Tehrik-e-Tabligh movement of Pakistan later claimed responsibility for the Barcelona plot on its Web site and in a video, while criticizing the presence of Spanish troops in Afghanistan, the prosecutor wrote.
Spain's interior minister and the investigating magistrate confirmed last year that an informant's testimony was a key part of the case against the suspects.
The prosecutor wrote, just before the trial, that "The discovery of the organization and the preparation of the attack was known, thanks to the statement of the protected witness, identified as F1."
Spanish news reports last year said the informant worked for French intelligence and had infiltrated the alleged Barcelona terror cell.
The prosecutor said the informant joined the Tehrik-e-Tabligh movement from France, later received military training in Pakistan and was finally sent to Barcelona, where he met the other suspects, learned of their plans and quickly informed authorities.
The alleged leaders of the cell were Mahroof Ahmed Mirza, who was to choose the place and time for the Barcelona attacks, and Mohammad Ayud Elahi Bibi. The prosecutor is seeking 18-year prison terms for them as leaders of a terrorist group and for possession of explosives.
Six other defendants face up to 16 years each in prison if convicted of membership in a terrorist group and possession of explosives. The rest would face lesser terms for other supporting roles.
But Interior Minister Alfredo Perez Rubalcaba said last year shortly after the arrests that police had not found enough explosives to have carried out the assault.
A court-appointed translator told CNN last year, after arraignments before a judge, that all the defendants had testified that they were innocent.
More than 300 suspected Islamic extremists have been arrested in Spain since the Madrid commuter train bombings that killed 191 people and wounded more than 1,800 on March 11, 2004, the interior minister has said.