PARIS — As twin hostage dramas ended violently on Friday with the deaths of armed jihadists who killed at least 13 people and traumatized France, the government faced gaping questions over the failure to thwart such brazen attacks, especially on a well-known target like the satirical newspaper Charlie Hebdo.

The French intelligence services knew that striking the newspaper and its editor, for their vulgar treatment of the Prophet Muhammad, had been a stated goal of Al Qaeda in the Arabian Peninsula, through its propaganda journal, Inspire. And they had the Kouachi brothers, Saïd, 34, and Chérif, 32, on their radar as previously involved in jihad-related activities, for which Chérif went to jail in 2008.

The French apparently also knew, or presumably should have known, either on their own or through close intelligence cooperation with the United States, that Saïd had traveled in 2011 to Yemen, where news reports on Friday said he had met with the American-born Anwar al-Awlaki, a member and propagandist for Al Qaeda in the Arabian Peninsula, who was later killed by an American drone strike.

But Yemen has been an American, not a French priority, intelligence analysts said on Friday. And with French security concentrating on the 1,000 to 2,000 French citizens who have traveled to fight in Iraq and Syria against the Syrian regime or with the Islamic State, it was likely that the Kouachi brothers and their friends — including Amedy Coulibaly, the man said to have been involved in the second hostage taking — were put lower on the priority list, the analysts said.

All three were reported killed in raids by the French police and security forces Friday evening.

Still, basic questions loomed about why the French had not monitored the Kouachi brothers more aggressively, what the brothers were doing between 2011 and now, and why Charlie Hebdo was not better protected. And those lapses raised the question of whether there had been a spectacular failure in American-French intelligence cooperation.

“The problem we face is that even though there are not that many radicalized Muslims in France, there are enough of them to make it difficult to physically follow everyone with a suspicious background,” said Camille Grand, a former French official and director of the Foundation for Strategic Research, a Paris-based group. “It’s one thing to listen to the phone calls or watch their travel, but it’s another to put someone under permanent physical surveillance, or even follow all their phone conversations full time for so many people.”

There simply are not enough police and security officials to keep full monitoring on everyone who goes through prison, said Jean-Charles Brisard from the French Center for Analysis of Terrorism, who had spoken to French security officials. The authorities had Chérif Kouachi under surveillance “for a period of time, but then they judged that there was no threat, or the threat was lower, and they had other priorities,” he said.

Given the 1,000 to 2,000 French citizens who have traveled to Iraq and Syria to fight, of whom perhaps 200 of them have returned, “it’s a problem of resources,” Mr. Brisard said. “To follow a person 24 hours a day you need at least 20 people. And you cannot impose surveillance on everyone, even legally it’s impossible.”

President François Hollande went on television again on Friday to try to reassure the nation, visiting the Interior Ministry to supervise the police action, which rapidly identified and cornered the suspects following the attack on Charlie Hebdo on Wednesday.

“France is going through a trying time,” he said, adding that “we have known for several months that there were attempts” at additional terrorist attacks, at least five of which have been thwarted in the last 18 months, the Interior Ministry said.

But why the attack on Charlie Hebdo was not thwarted will preoccupy French security and the French public.

The attacks also are likely to aggravate the political problems of Mr. Hollande, already considered weak and indecisive.

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