It is war and should be treated as war
It is not a law enforcement style crime.
The aggressors in this need to be treated as any other war criminal and enemy combatant.
My wife has lived and studied in Madrid and loves that city very much. She may go there this summer for classes. This is very troubling for her on a personal level. Our prayers and sympathies go out to the victims and their families, as well as to the people of Spain, to have strength to withstand this vicious attack.
Ed