FBI warned MI5 in January about this guy
http://www.independent.co.uk/news/uk/home-news/fbi-warned-mi5-january-manchester-attack-bomber-salman-abedi-manchester-arena-a7760756.html
http://www.independent.co.uk/news/uk/home-news/fbi-warned-mi5-january-manchester-attack-bomber-salman-abedi-manchester-arena-a7760756.html