Eagles of Death Metal was in full swing at the Bataclan concert hall on November 13th, 2015, when armed men wearing explosive belts stormed in and killed 90 people.
Close to a year later on September 10th, the US rock group played at the Apolo concert hall in Barcelona.
Under high alert, police stopped a Moroccan man in front of the hall and asked him for his ID, said a spokesman for police in the northeastern region of Catalonia where Barcelona is located.
He told AFP that on identifying him, police discovered alleged links to people involved in the Brussels airport and metro attacks last year that left 32 people dead and more than 320 wounded.
The attacks were led by an Islamic State cell that was also responsible for the carnage in Paris in November 2015.
“He was put under surveillance, as was his entourage,” the police spokesman said.
It is not known why the suspect was in front of the Barcelona concert hall, or whether it was pure coincidence.
But the police spokesman said authorities don't believe he was planning any kind of attack that night.
The suspects arrested in Catalonia are due to be questioned by a judge in Madrid on Thursday.
They are also being investigated for drug trafficking, robbery and other crimes.