Kirill Serebrennikov was put under house arrest in a controversial embezzlement case.
Dead imam recruited young men from the Moroccan immigrant community in the mountain town of Ripoll.
The suspect had been sought since Thursday, when a van plowed into the crowded La Rambla promenade in Barcelona.
The move came as tough-talking Anatoly Antonov was named Moscow’s new U.S. ambassador.
But French police said the incident was not initially treated as a terrorism investigation.
As the driver of the car in last week’s attack continued to elude police, attention also turned to a missing imam in the 12 suspects’ home town.
Usually, terrorist attacks immediately trigger spikes in anti-Muslim sentiment. Not in this Spanish city.
The French elected him by a landslide in May. Now his poll standing is near Trump’s.
Authorities believe that at least eight suspects were involved in the Barcelona and Cambrils incidents. At least one remains at large, and the fate of the van driver in the Barcelona attack is still unknown.
Parents fear their sons were radicalized by a visiting cleric who possibly brainwashed gullible youngsters who spoke better Spanish than Arabic.
Cold War-era tensions shaping de-Nazification resurface in debates over communist symbols.
Two people in Finland were killed and eight others wounded Friday when an 18-year-old Moroccan man went on a stabbing rampage in the southwestern city of Turku, authorities said.
Police foiled another vehicle attack just to the south, killing five men in a car that also ran over people.
For many who witnessed the carnage, it is the image of the white delivery van — used to mow people down — that remains the most haunting.
The Islamic State claims responsibility for initial attack, in Las Ramblas district.