(CNSNews.com) - Spain's history and a reluctance to jump to conclusions had officials in Madrid blaming Basque separatists for Thursday's deadly train bombings in the city, but the discovery of a van containing detonators and a tape with verses of the Qur'an in Arabic indicates that other lines of inquiry would not be ruled out.
Adding to the suspicions of an Islamist link, a London-based Arabic newspaper used before by al Qaeda to get its messages out to the world said it had received a letter, purportedly from the network, claiming responsibility for the attack in Spain.
"We have succeeded in infiltrating the heart of crusader Europe and struck one of the bases of the crusader alliance," it said, according to Reuters.
The coordinated bombings that killed at least 190 people and injured more than 1,300, is believed to be the most deadly in Europe since the Pan Am bombing over Lockerbie, Scotland in 1988.
Although the Basque terrorist group ETA remains the obvious suspect, some terror experts have noted that the modus operandi of the attack, synchronized bombings causing massive devastation and no prior warning given, differed from that of ETA.
The Basque group, the acronym stands for Euzkadi Ta Askatasuna (Basque fatherland and freedom), has suffered from arrests of key leaders, and reports cite police as estimating that its activist strength is down to below 250.
Officials have been boasting that the group, which has carried out bombings, kidnappings and assassinations since the late 1960s, was on its last legs.
Batasuna, an outlawed political party regarded as the political wing of ETA, raised doubt that ETA would have been responsible. Batasuna party leader Arnaldo Otegi was quoted as blaming the "Arab resistance" for the bombings.
Nonetheless, with a general election just days away, ETA remains the likeliest suspect, and some analysts suggested that it had possibly learned lessons from al Qaeda atrocities about how to make an impact, for maximum advantage.
Spain's Interior Minister, Angel Acebes said earlier that "ETA were looking to carry out a massacre ... and they have achieved their objective."
Hours later, however, Acebes announced that police acting on a citizen's tip-off had found a van in a town outside Madrid, and on the front seat were seven detonators and an Arabic-language tape of verses from the Qur'an.
"Because of this, I have just given instructions to the security forces not to rule out any line of investigation," he said, adding that ETA remained the "main line of investigation."
The town where the van was found, Alcala de Henares, was the originating point for three of the four trains bombed on Thursday.
Spain has been a close ally of the U.S. in international efforts to defeat terrorism, supporting Washington in Iraq and in an anti-proliferation initiative involving interdiction of suspect ships.
An audio tape attributed to al Qaeda leader Osama bin Laden, sent to the Arabic al-Jazeera television network last October, carried a warning against the U.S. and other countries supporting it in the Iraq campaign.
"We reserve the right to retaliate at the proper time and place against all countries that take part in this unjust war, namely Britain, Spain, Australia, Poland, Japan and Italy," said the man identified by al-Jazeera as bin Laden.
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