We can't expect them to be infallible, that's completely unrealistic. You mentioned the Brazillian, literally the day before there was a failed bomb attack, two weeks before a successful one! How many bomb attacks have been stopped by Security Services since? MI5, CO19, SFs were twitchy as feck in 2005, we were being attacked left right and center. They made one mistake through showing 100% vigilance. They were that concerned that they has SFs depolyed to intercept, those boys don't have a policy of making arrests!
This Duggan lad was hardly innocent like the Brazillian. Intelligence is no