When Terror Suspects Slip Under The Radar

Thousands of people are on 'watch lists' or 'no-fly lists'. However, predicting when they will decide to launch an attack is notoriously difficult.

All four suspects involved in the French attacks were on the security radar and had links to terrorist organisations.

It is a similar scenario to the one faced by the UK security officials with the Woolwich attack when Drummer Lee Rigby was barbarically killed in the street.

The killers, Michael Adebolajo and Michael Adebowale, were both known to the UK security services, who had even tried to recruit Adebolajo. Yet they were unable to prevent the murder on a busy London street.

Adebolajo resented UK and US foreign policy and made sure he explained his views during his trial at the Old Bailey.

Similarly, when Paris terrorist Cherif Kouachi was jailed for 18 months for his part in sending volunteers to fight alongside al Qaeda in Iraq between 2003 and 2005, he used US abuse of prisoners in Iraq as justification for his actions.

France's interior minister, Bernard Cazeneuve, is calling for "extreme vigilance" and said after an emergency security meeting "we are exposed to risks" as France maintains its terror alert system at the highest level in the Paris region.

More often than not plots are foiled before they can be carried out.

The French Prime Minister has acknowledged, though, that despite his country's best efforts the loss of the lives of 17 citizens can only be seen as a "failure in intelligence".