How could a pair of brothers with such strong known links to terrorist networks manage to successfully pull off France's deadliest terrorist attack in half a century?
As the dust begins to settle after days of shootings, hijackings, hostage takings and terror in and around Paris this week, questions are beginning to mount as to how two of the attackers were able to slip through the cracks of France's intelligence network.
Security experts say officials may need to change their protocol for surveillance and thwarting planned attacks, such as the one on the Charlie Hebdo offices.
Brothers Cherif and Said Kouachi - born in France to Algerian immigrants - were known to French authorities as potential threats for years, and were both on the US government's "no fly" list, as well as a number of other FBI terror watch lists.
German Interior Minister Thomas de Maiziere said on Friday that both brothers had been on a watchlist put together by countries in the European Union's passport-free Schengen travel zone.
Yemeni officials, meanwhile, confirmed that Said, 34, had trained in Yemen with Al Qaeda.
Cherif, 32, was arrested in France in 2005 for his role in recruiting militants to fight in Iraq, and was sentenced to three years in prison. In 2010, he was arrested again in connection with the failed jailbreak of a mastermind behind the 1995 Paris bombings, which killed eight people and injured more than 200. Cherif was not charged, due to lack of evidence.
The former pizza deliveryman even featured in a 2005 French television documentary about militants, called "Pièces à conviction", or "Elements of Evidence." He was portrayed as a fresh young member of a group who followed a self-proclaimed spiritual leader, and was training to become a Muslim holy warrior.
The cleric "told me that [holy] texts prove the benefits of suicide attacks," he says in the program. "It's written in the texts that it's good to die as a martyr."
Then, seeking to lower their profile, the Kouachi brothers suddenly went quiet.
"They deceive us"
"They were under surveillance, but not all of the time," said Eric Denece, director of the Paris-based French Center for Intelligence Research. "The problem with this type of surveillance is that these groups know the patterns and how they are being monitored. So they stopped having regular meetings, they stopped communication with other terrorist organizations, and so security decided to stop part of the surveillance."
While the brothers were red-flagged when they were involved in radical activity, they had since remained quiet and had not broken any French laws - slipping off the authorities' radar somewhat.
"The problem with this is that the French security services need to change the way they do their monitoring of terrorists," Denece said. "We have to understand the people we are fighting, and how they deceive us. We have to change the way we manage them."
Stephanie Pezard, a French security policy expert at the Washington-based nonprofit security group Rand, said that internal investigations could reveal holes. "The concern is that maybe intelligence services had not picked up on important facts on these individuals, and perhaps could have done a better job monitoring them," she told DW.
"They were definitely on the sight of the French services, but now the question is how often they can monitor them - they cannot monitor everyone every day. But how often? They may have done their best, or they may have missed something," Pezard added.
At least 1,200 citizens are or have been involved in the Syrian war, French interior minister Bernard Cazeneuve told parliament last month. He said about 60 had been killed and 185 had returned to France - of whom 82 were in jail and 36 others under some form of judicial control.
Soul searching in France
Jack Cloonan, a former FBI special agent, thinks the events this week will forever change how France addresses its surveillance programs. "The French government will now have to do some very serious soul searching," said Cloonan, who now works with the global crisis management group red24.
"The US was criticized after September 11 for not being able to connect the dots, and treating these issues as law enforcement rather than issues of national security. This will now shift France's strategy to predictive analysis, which is something they will be reluctant to do," said Cloonan, stressing the French are "loath to put into practice something like the Patriot Act, or electronic surveillance or data mining."
"How will they predict what is planned by two or three people who are loosely associated to groups and can be self-radicalized? How much are the French willing to give up a bit of their personal liberty to protect themselves?"
Amateur, homegrown terrorism
It's not a surprise the Kouachi brothers' plans went undetected, according to Jean-Claude Allard, director of research for the French Institute for International and Strategic Affairs in Paris.
"When you have something like September 11, with bombs on planes or trains, that is complex and requires logistics that make it much easier for police to track," Allard said.
"During the last year, French police have detected a lot of this type of chatter related to this kind of preparation. But in this case, when you have just two young men who are not very prepared - one forgot his identification in the getaway vehicle, remember - if there is no action immediately prior, it is very difficult to find these people," said Allard.
But it is these very people - homegrown, amateur - who are the most unpredictable and dangerous, Cloonan insists.
"It is these disenfranchised youth who feel the sting of alienation and want to retaliate - and what we see playing out before us is an attempt to humiliate the French government," Cloonan said.
"This is who the government should be most afraid of, and there needs to be a serious analysis and re-engineering of their lives to find out what led them to this time. To just engage in robust security operations and not take into consideration what has been done wrong in a societal context does not accomplish the ultimate goal."
Experts agree that French security forces are equipped to handle attacks as they happen, as proven by the way elite forces fanned out across Paris and the surrounding regions affected this week. French Interior Minister Bernard Cazeneuve announced Friday that 88,000 forces had been mobilized and that an international counter-terrorism meeting would take place in Paris on Sunday.
Paris police, national police, the General Directorate for Internal Security and others have led the counterterrorism operation this week, Pezard said. That includes an elite Swat-team-like force specializing in hostage situations and combating terrorism, known as Research Assistance Intervention Dissuasion.
"We cannot say that it is due at all to lack of manpower - they have deployed lots of military to police in Paris and Picardy [where the manhunt had been focused]," Pezard said. "It really shows how serious the government is taking this."