Widely seen as Europe's version of Sept. 11, 2001, the explosions on four Madrid commuter trains left 191 people dead and more than 1,500 injured.
Although about 75 people have been arrested in the attacks, and 23 remain in prison, European security officials lament a lack of coordination among various police agencies on the continent, the Washington Post reported.
"We are on the right way, but we didn't go far enough," said Berndt Georg Thamm, a terrorism expert in Germany who works with the country's security agencies and military.
"The big bang of 11 March pushed the European Union in the right direction," he said, but added it would "take some years before we have complete international, and also national, information-centered cooperation."
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