The Spanish town of Cambrils has previous links to terrorism having hosted a meeting between a pilot in the 9/11 attacks and an al Qaeda plotter.
Seven people were injured in the coastal town overnight in a second vehicle attack following the atrocity in Barcelona.
It is the second time the town has been linked to terrorism after Mohammed Atta, who piloted the first hijacked airliner into the World Trade Center, visited Cambrils before the 2001 atrocity.
He drove from Madrid to the seaside town after collecting fellow conspirator Ramzi bin al-Shibh, and they are thought to have spent a night at a hotel there.
:: LIVE: Spanish terror attack latest updates
It is unknown where the two men went when they left the town, but they are believed to have spent several days together planning the 9/11 attack.
Al Qaeda chose bin al-Shibh to be one of the September 11 hijackers but he was unable to obtain a US visa.
Instead the Yemeni helped organise the attacks, finding flight schools for the hijackers in the US and arranging financing for the operation.
:: Spain terror attacks: What we know so far
Bin al-Shibh reportedly met Egyptian-born Atta while they were studying in Germany in the 1990s.
He was arrested in Pakistan in 2002 and taken to Guantanamo Bay, where he is still being held today.
US authorities accused him of filming a “martyr video” in preparation for September 11 and being a “key facilitator” of the attacks.