The world can breathe a little easier knowing that Abdelhamid Abaaoud, mastermind of the Paris terror attacks, was killed in a firefight with French authorities yesterday.

Abaaoud’s terror attacks, which claimed 129 innocent lives last Friday, highlight the continued risk posed by the terrorist group known as the Islamic State—especially to western European nations who have had large numbers of citizens traveling to Iraq and Syria.

Missed Opportunities to Catch Abaaoud

The attacks also highlight missed opportunities for security services to stop the plot before it took place and once again expose deep holes within Europe’s Schengen visa-free area.

Finding and eliminating a terrorist ringleader who is suspected of plotting both the November Paris attacks and numerous other plots (including an attempted attack on a church in France, a plot against Belgian security services, and the Amsterdam to Paris train attack) is a very good thing.

It also took quite a bit of courage: According to reports, French SWAT teams fired 5,000 rounds of ammunition in Thursday’s raid against Abaaoud.

However, Abaaoud was just a leader of one ISIS cell; it will not end the threat from Islamic terrorism.

More troubling still are the multiple missed opportunities to kill or capture Abaaoud.

He traveled to Syria in 2014 to fight alongside ISIS and returned to Europe at the end of 2014. Intelligence services tracked him to Greece via a phone call he made to an inmate in Belgium, but the information did not lead to his arrest.

Despite launching major operations in January 2015 to capture Abaaoud, it is suspected he escaped back to Syria in January 2015. One former French counter-terrorism specialist is quoted as saying of the intelligence failures:

… someone has screwed up … either no one saw anything, and that’s a big worry, or we saw things and we didn’t understand them, which is also a problem, or we saw things and despite everything they were able to carry out the attack.

Security Services Overwhelmed

The sheer scale of foreign fighters traveling to Iraq and Syria and returning to the West to commit atrocities has in part overwhelmed security services. Additionally, a major difficulty in foiling the movement of terrorists is Europe’s visa- and border control-free Schengen Area.

Europe’s visa-free Schengen Area, which is a visa- and border control-free area among 26 European nations, means that once a person gains entry into a Schengen-zone country, such as Greece, he can then freely travel to any other Schengen-zone nation, including France and Belgium.

The Paris terror attacks appear to have been plotted and organized in Belgium, before the terrorists slipped across the border with France to commit them. A lack of border control may have helped effect the atrocities.

Furthermore, the Schengen zone means foreign fighters often leave or enter Europe through nations more likely to have porous border security before traveling on to places like Belgium, France, and Germany to commit acts of terror.