The imam thought to have masterminded the deadly Barcelona terror attacks shared a flat with an al Qaeda terror recruiter and had links to the 2004 Islamist bombings in Madrid, the Spanish press has reported.
Abdelbaki Es Satty, 40, is suspected of radicalising a number of the killers and handled explosives that the cell plotted to make into van bombs. An accidental explosion killed him just days before the attack.
He was also in Belgium between January and March last year, shortly before Islamic State-inspired terrorists attacked Brussels airport and Maalbeek metro station, killing 32 people.
He lived with Mohammed Mrabet Fahsi in Vilanova i la Geltru, a coastal town about 30 miles southwest of Barcelona between 2003 and 2005.
Mr. Fahsi was accused of recruiting fighters for jihadist causes in Iraq and Syria. He was arrested in 2006 in Spain as he prepared to move to the United Kingdom, and jailed for funding terrorism.
A Salafi mosque in the town of Vilanova i la Geltru, is reported to have been known for preaching a radical message.
Three other al Qaeda suspects also stayed in the flat, including Belgacem Bellil, an Algerian who blew himself up in Iraq in 2003, killing 14 Italians and nine Iraqis.
The radical group living in Vilanova i la Geltru had contact with another terror cell in Santa Coloma de Gramenet, north of Barcelona, which helped the Madrid bombers to escape, local media reported.
Es Satty spent at least two years in prison from 2012 for smuggling cannabis between North Africa and Spain, El Periodico newspaper reported. There, he befriended Rachid Aglif, who was jailed for 18 years for the Madrid atrocity in which 192 people died.
The imam may not have been the only terrorist suspected of travelling across Europe, taking advantage of open borders.