Since the horrific terrorist attacks in Paris, much has come to light about who carried them out and where did they came from. We also learned on Tuesday from French officials that they believe a suicide attack was planned against the financial district in Paris.
After the police raids in Europe slow down, we will begin to analyze what took place to figure out how these awful things could happen and how they can be prevented.
Here is what we know so far:
-- The alleged mastermind of the attack, Abdelhamid Abaaoud, was able to evade capture and remain at large despite being one of Belgium's most wanted terrorists. Abaaoud was also believed to be linked to the failed train attack in August and an attack on a Jewish museum in 2014. He was killed in a French raid on Wednesday while planning suicide attacks. He also visited scenes of the attacks in Paris on Friday November 13 while first responders and police were still present.
-- One of the attackers, Ismael Mostefai, returned to France even after authorities in Turkey warned that he had disappeared while there, possibly traveling to Syria.
-- Another attacker, Salah Abdeslam, was stopped at the French-Belgian border the morning following the attack but was released. How do you stop someone who's a terrorist if you don't know if he or she is a terrorist?
The Irish Republican Army once said, "...remember we only have to be lucky once -- you will have to be lucky always." This quote is apt for the Paris attacks. Intelligence and security services must be perfect all the time -- a single failure can result in tragedy.
It is likely that an intelligence gap occurred in Paris, given the level of radicalization in certain neighborhoods in Brussels and Paris, coupled with ISIS propaganda campaigns and the deluge of refugees coming into the European Union.
Some of the attackers were known to French and Belgian authorities before November 13, which begs the question: At which point do you intervene? Just as in America, the European Union tries to balance privacy, security and the freedom of expression. Even more sobering still is the idea that some attackers were unknown to the security services.
It is clear that some connections were not made or insufficient information was available for the security services to act at the time. Since the attack, we have seen hundreds of raids on suspects with ties to the attack, or possessing radical and violent beliefs. Such operations are impossible without existing data, so the French services have at least some knowledge of many of these people.
Part of the problem is the way the adversary has evolved.
ISIS represents not a new threat, but the latest incarnation of the continuing threat of militant Islam. Whereas al Qaeda operates as a traditional terrorist network with cells reporting to an established hierarchy, ISIS is far more opaque and decentralized. ISIS is a network of influence; al Qaeda is a network of command.
Where al Qaeda has been focused on achieving spectacular attacks such as 9/11, ISIS is happy to have a handful of terrorists grab guns and murder people at random. Large-scale attacks that al Qaeda prefers take months to plan, between dozens of people and cost large amounts of money. As a result, each of their operational pieces present a chance for Western intelligence services to identify and disrupt. ISIS plans have less of a footprint.
This difference makes combating ISIS all the more difficult. ISIS terrorists are using the fabric of Western society against it: open borders, freedom of travel and technological innovations. How can you keep track of all of the individuals entering and exiting Syria with such massive borders? How can you identify domestic passport holders who have trained in Syria and are returning home? How do you find and interdict self-radicalized individuals who access ISIS propaganda in the comfort of their own homes?
Combating al Qaeda was challenging enough and required the development of a whole new approach to national security -- sustained domestic counterterrorism efforts and aggressive kinetic campaigns overseas. But now the model is being inverted -- kinetic action alone overseas is insufficient. Where al Qaeda militants often were "different" enough to stand out, ISIS has embedded itself in the West through the use of our own citizens and technology platforms. And despite 33 successful attacks outside of Syria and Iraq, we still do not have an adequate strategy to address the threat posed by ISIS.
The analysis of the intelligence gaps will continue in the coming days, but Western intelligence will need to re-examine what it knew and didn't.
These small-scale, high-impact attacks are very difficult to prevent. What you can do is apply constant, unyielding pressure on the terrorists where they live, plan and train for these attacks.
Mike Rogers is a former chairman of the House Permanent Select Committee on Intelligence, a host of the Westwood One radio program Something to Think About and a CNN national security commentator. The opinions expressed in this commentary are solely those of the author.