BARCELONA, Spain — Police put up scores of roadblocks across northeast Spain on Sunday in hopes of capturing a fugitive suspect from the 12-member Islamic extremist cell that staged two vehicle attacks and plotted much deadlier carnage using explosives favored by Islamic State militants. Complicating the manhunt, though, was the fact that police have so far been unable to officially identify who exactly is at large. While police have identified the 12 members of the cell, three people remain unaccounted for: two believed killed when the house where the plot was being hatched exploded Wednesday, and a suspected fugitive, Catalan police official Josep Lluis Trapero told reporters Sunday. Trapero declined to confirm that Younes Abouyaaquoub, a 22-year-old Moroccan, was the one at large and the suspected driver of the van that plowed down Barcelona’s Las Ramblas promenade Thursday, killing 13 people and injuring 120.