When an attack is carried out, it is logically a failure of the whole structure that is in charge of preventing its commission. In that prospect, intelligence plays an essential role in identifying hostile individuals, collecting useful information, and building up a sufficient bundle of evidence to justify the arrest of suspects.
The Manchester (UK) attack on May 22, 2017 that killed 22 people at the end of a concert by the American singer Ariana Grande and that was claimed by the Islamic State (ISIS) underlined ongoing flaws within the intelligence community.
Indeed, according to the BBC, British domestic intelligence (MI5) was alerted at least three times about the extremism of Salman Abedi, who died by operating his suicide bomb in Manchester. A post-attack investigation would have therefore been opened to find out why MI5 did not see fit to intensify Abedi’s surveillance and with a view to identifying possible failures.
If such a procedure is useful it must not, however, remove the decisive responsibility of political leaders who charge intelligence with an impossible mission by keeping porous borders for hostile individuals and not sufficiently sanctioning the extremist ideology that irrigates the terrorist nebula.
Manchester attacks: MI5 probes bomber ‘warnings’ (BBC, May 29, 2017)