What & Who discovers terrorist plots?

[davidbfpo]

Rather unusual as the discovery was made by a non-UK national:

Hussain's activities came to the attention of counter terrorism police after a man reported receiving an email from him. The court heard how the witness, who lives outside the UK, emailed the Home Office in March 2017 after receiving a private message on Facebook, from someone he did not know, inciting him to join Daesh.
Commander Dean Haydon, head of the Met Police Counter Terrorism Command, said: "This investigation started with one conscientious individual trusting his instincts and reporting something suspicious. He could have ignored the message Hussain sent him but instead he took a screenshot of the message and contacted the UK authorities immediately. It is in great part thanks to him that police were able to bring Hussain to justice."

Link:http://news.met.police.uk/news/man-j...ffences-296161