Al-Qaida suspicions
Immediately following the attacks, commentators began to suggest that al-Qaida, and not ETA, could have been responsible. Arnaldo Otegui, leader of Batasuna, said he could not believe the attacks were the work of ETA, "even as a hypothesis" and suggested that the "Arab resistance" was the most probable perpetrator. On the evening of 11 March, Acebes told a news conference that a van, stolen on February 28 and containing several detonators and an Arabic-language cassette tape with Koranic verses, had been found in the town of Alcalá de Henares, where three of the four bombed trains originated and all four stopped. However, the tape was commercially available and contained no material specific to the attacks; thus it could have been planted to confuse the investigators.
Al-Qaida had certainly shown an interest in Spain in the period preceding the attacks. In November 2001, Spanish authorities arrested eight men suspected of being al-Qaida operatives, one of whom reportedly had past links with Basque ETA. Osama bin Laden issued a public threat in October 2003 to carry out suicide bombings against any countries joining the US-led invasion of Iraq: "We reserve the right to retaliate at the appropriate time and place against all countries involved, especially Britain, Spain, Australia, Poland, Japan and Italy." At the time, Spain had some 1,300 soldiers stationed on Iraqi soil. In addition, bin Laden had spoken earlier of wishing to return the southern Spanish region of Andalusia to Muslim control, reversing the Reconquista of 1492.
Precedent
Information made public on 12 March by the Norwegian Defence Research Establishment (FFI) revealed that intelligence agencies had known for two months that a terrorist attack was being planned against a country entering into an election period. However, they mistakenly believed that country to be Iraq. The supporting documents, written in Arabic, belonged to a senior al-Qaida leader, Yusuf al-Airi, and had been obtained by the FFI over the Internet, after his death in May 2003.
According to the FFI Muslim fundamentalism expert Thomas Hegghammer, the documents described in detail the tactics and strategies that were to be employed. The tactic was to break the U.S.-led occupation of Iraq by performing successive strikes on the co-operating member states, starting with the one which would most easily lose its resolve to keep its troops stationed in Iraq, and then following on with the rest. The Iraq war was very unpopular in Spain, and so this would make a likely first target.