15 years ago today on September 11, 2001, the world became witness to an unimaginable horror, the sight of New Yorks skyline ablaze fundamentally changed how we as a society view terrorism. Today we are still struggling with the threat of terror attacks as they seem to be coming fast and furious, from Boston, Paris, Brussels, San Bernardino, Orlando and Nice it is obvious that we have now entered a new age of crowd-sourced violence which is rapidly spread with the help of the internet.

In this PBS, NOVA special we trace the evolution of the tactics employed by todays terrorists, starting off with the World Trade Centre right up until the most recent attacks seen in Nice, France. How is it that these radical organisations have grown into such propaganda machines, using social media as a primary weapon for cultivating an army of self-radicalized killers?

What is really going on inside the mind of this new breed of terrorist and how can we help aid law enforcement to cope with this new form of threat?