overnight a new arrest in the london attack investigation. this comes as big questions emerge for british intelligence. we learned the ring leader of saturday's deadly attack was a high priority for law enforcement in 2015. it was part of an effort dismanhattan all group of extremists in the uk who actively support isis. let's go live to one of the attackers in a documentary entitled "jihadis next door." what happened? >> reporter: big questions for supreme cou security forces. theresa may sent out her foreign secretary to conduct many interviews yesterday and he acknowledgeed should be some kind of review why this individual was missed because as you pointed out, he was well-known in the media circle