How al-Qaeda became main suspects: On Saturday night, Madrid police were led to a video tape left in a waste bin near the largest Madrid mosque, writes Jane Walker in Madrid.
It contained a grim message from a man speaking Arabic with a Moroccan accent claiming to be Abu Dujan al Afgani, of al-Qaeda's military wing in Europe. "We declare our responsibility for what happened in Madrid. It is our response to your collaboration with the criminal Bush and his allies. There will be more if Allah wills it. You love life, we love death."
When the chain of simultaneous bombs exploded on three crowded commuter trains early on Thursday morning, killing 200 people, most people's minds turned to the Basque terrorist organisation Eta who had threatened to carry out an attack in the days before yesterday's election.
Although Eta has killed some 800 people over the past 40 years, it has never carried out an attack like the one in Madrid this week. It was so out of character some people immediately suspected an Arab fundamentalist organisation, and late on Saturday night they had further proof for their suspicions.
The government had no doubt it was the work of the Basque terrorists. Mr José María Aznar, the outgoing prime minister, declared: "This organisation (Eta) is there to kill as many people as it can and sometimes they succeed."
His interior minister, Mr Angel Acebes, agreed: "It bears all the hallmarks of Eta." He was still blaming Eta some 12 hours later, even as he announced the discovery of a stolen van outside the station where the terrorists are believed to have put the bomb-containing bags on the trains.
Inside the van police found traces of explosives, seven copper detonators, a bag containing items of clothing, and an audio tape in Arabic with verses of the Koran which Mr Acebes shrugged off as "the kind anyone could use for Islamic studies, not difficult to obtain". But it forced the authorities to open a second line of investigation into possible Arab connections.
And Mr Acebes expressed doubts when the London based Al-Quds al Arabi newspaper was e-mailed an alleged confession: "We have succeeded in infiltrating the heart of crusader Europe," said the message.
A major breakthrough came when police officer Mr Jacobo Barrerowas sifting through the wrecked carriages in El Pozo station. He picked up a canvas sports bag, looked inside to see if it carried any identification, and instead saw an unexploded bomb consisting of 10 kilos of Goma 2 dynamite attached to a detonator and a mobile phone.
"It was the most important clue to date. We had fingerprints and the mobile phone with its SIM card to analyse," Mr Ignacio Astarloa, Secretary of State for Security told the Irish Times on Saturday.
And it was the phone card which led the police to their first arrests. On Saturday evening three Moroccans and two Indians were arrested in Madrid, and two Spaniard nationals of Indian origin were detained in Barcelona for questioning in connection with the sale of illegal mobile phones and forged SIM cards.
All five are being held under anti-terrorist legislation. They may be held for up to five days before appearing before a judge.