Did authorities miss signs before the Paris attacks?

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PARIS (CNN) –– In January, terror descended on the French capital when black-clad gunmen stormed the offices of satirical magazine Charlie Hebdo, killing magazine staff and triggering a three-day manhunt.

A crackdown on extremists was promised — yet within the year, Islamist terrorists have struck Paris again in an even deadlier attack, killing 129 people in coordinated terror attacks Friday.

A spokeswoman for France’s ruling Socialist Party has conceded there was a failure of intelligence and that improved surveillance measures in the wake of the Hebdo attacks were not yet fully operational.

CNN international diplomatic editor Nic Robertson explains how France’s security and intelligence apparatus, once vaunted as a counterterror powerhouse, could have failed to prevent such an attack.

Why wasn’t the attack plan spotted? Was it a failure of intelligence or did the attackers use distinctly new methods to avoid detection?

There were two fundamental reasons. The attackers are believed to have used encrypted means of communication. But they were also below the radar because they were able to sneak back into the country undetected.

How is that so, when at least three of the attackers were known radicals?

It appears that the plot didn’t trigger an alert because the French authorities didn’t know some of them were in the country.

Part of it does seem to be that there is free and easy travel across the border. (France and 25 other European countries are party to the Schengen Agreement, which allows for passport-free travel across much of the continent.)

That seems to be, unfortunately for Schengen Europe, one of the issues that’s highlighted — you just don’t know when these people are traveling across the border.

There are clearly issues at the European level. If a known radical returns from fighting in Syria or Iraq, for example, and he enters Europe via Greece, then the authorities in his own country would be informed.

But if a French radical returned from fighting and went to Belgium, the Belgians would have no idea he was coming or that they should be on the lookout for him, unless he was already on their radar.

Upshot: The European system of monitoring people who go to fight for ISIS is not up to the task.

French President Francois Hollande has said that the plot was organized in Belgium, and the authorities in Brussels are aware the country has a jihadist problem. Why were the attackers not on the radar there?

As far as we know, some of the French attackers were able to stay below the radar because they had been in Belgium and the Belgian authorities didn’t know they were a threat.

Part of this is due to lack of information-sharing. Had the French been connecting the dots with other countries more, they should have been aware that these guys were back on their patch. It’s a glaring failure.

But part of the reason that the Belgians didn’t have more information and weren’t able to inform the French is because their own security services are quite divided, perhaps more than any other European nation. It’s because of the nature of the country, of being forged from two distinct linguistic communities.

Belgian authorities admit they didn’t know these terrorists had returned from Syria.

But France and Belgium are European neighbors.

It’s alarming.

Precisely how and where the system is breaking down is hard to know at this stage.

It’s hard to know how dysfunctional that relationship is, but there are indications that there is tension on both sides in the way it’s not working. Recriminations are already beginning.

Some of the attackers are believed to have fought in Syria, then slipped back into Europe. How is this possible, given the known threat posed by returning foreign fighters?

There seems to be solid evidence that at least one attacker had false ID papers. He seems to have been able to smuggle himself recently, which is alarming.

It does appear to show a clear intent to use the arrival of refugees as a cover to get themselves back into Europe and raises questions about how many more returning jihadists have done this.

France suffered terror attacks in January this year. Has it not stepped up its intelligence response?

You have the example of (accused Bataclan attacker) Ismael Omar Mostefai, who was known to be radicalized but not believed to be associated with terrorists. There’s an intelligence failure there that can probably be attributed to not having enough intelligence assets and resources.

He slipped out of the country and went to Turkey. The Turkish authorities asked the French questions about him and the Turks didn’t get any answer back from the French, as recently as June this year, according to Turkish authorities.

That’s another failure in international cooperation, this time with a country which is an important entry point into Syria for European jihadists.

This kind of thing should’ve been at a more prioritized level. One of the things that came out of the NATO summit in Wales last September was an agreement for NATO nations — which include Belgium, Turkey and France — to be more proactive and share information better. I’d say that that promise from NATO leaders hasn’t been followed through effectively.

How underresourced are French authorities when it comes to combating the jihadist threat?

Woefully underresourced, it seems.

Hollande said he was going to increase those services by another 5,000 people over the next five years and said that will bring the total to 10,000. Well, that shows they’re at half-strength now — and a five-year plan is pretty slow when you have two major attacks in a year and another attack foiled.

What we’re told by intelligence officials is that it takes 15 to 20 people to monitor one suspect 24 hours a day. They have 11,000 people on their “fiche S” list, used to flag individuals considered a threat to national security and who they believe are radicalized. Of those, 5,000 have been elevated to an additional level of concern. Adding to that hundreds, perhaps more than 1,000, who have gone to Syria and Iraq, of whom about half have returned.

What is the rest of the intelligence community saying?

People are worried. People are genuinely worried and they’ll be even more worried after Wednesday morning’s thwarted attack, because they genuinely feel they don’t know what’s going to happen next.

CNN’s Tim Hume contributed to this report.