Four sets of brothers have been linked to the Spain attacks, and brothers were involved in Paris, Boston and 9/11
As is so often the case in terrorist cells, the group that brought carnage to north-east Spain last week – killing 15 people and injuring more than 130 – included several sets of brothers.
Younes Abouyaaqoub, 22, has been identified by police as the driver of the van that sped down Las Ramblas on Thursday. He was shot dead by police in Subirats, a town 30 miles west of Barcelona, on Monday. His brother Housainne, 19, was among the five men shot dead by police in the coastal town of Cambrils hours later after the car in which they were travelling ploughed into a group of pedestrians.