The official said Kouachi's motivation for waiting so long -- possibly since 2011 -- to launch an attack was not clear.
U.S. officials Sunday said American authorities don't have evidence yet directly linking AQAP to specifically ordering the Paris attack last week at the offices of the satirical magaine. "We don't have credible information, at least as yet, to indicate who was responsible, who sponsored this act. That is clearly one of the things that we have to make a determination of," Attorney General Eric Holder told CNN's Gloria Borger on "State of the Union."
French security agencies had been monitoring Said Kouachi and his brother, Cherif, but stopped months before the two carried out the attack that left 12 people dead. The French monitoring faded despite a previous tip-off from American intelligence agencies that one of them had likely trained with al Qaeda in Yemen, a French news magazine reported Saturday.
Said Kouachi is suspected of slipping off for terror training in Yemen during a trip he made with another French national to Oman between July 25 and August 15 in 2011, according to multiple French officials who spoke to L'Express national security reporter Eric Pelletier
. Pelletier shared the details of his reporting with CNN.
U.S. agencies developed intelligence suggesting a high probability that Said Kouachi slipped across to Yemen during the trip to Oman and informed their French counterparts, according to Pelletier's French sources.
The French immediately responded by placing Said Kouachi under surveillance in late November 2011 by issuing a "Fiche de Surveillance" -- a surveillance notice, multiple French officials told Pelletier. The surveillance was conducted by both DGSI -- France's domestic security service -- and later by the judicial police. Wiretaps were authorized for his cell phones and that of his brother Cherif.
A U.S. official told CNN last week that the initial assessment was that Said Kouachi's 2011 travel lasted three or more months and that he is believed to have trained with al Qaeda in Yemen during that period.
But the surveillance of Said was terminated in June 2014 because French security services judged him no longer dangerous, Pelletier was told. The surveillance of Cherif Koachi stopped earlier -- at the end of 2013. Cherif's phone calls suggested he had disengaged with violent extremism and was focusing on counterfeiting clothing and shoes.
French intelligence authorities believe there is a strong probability Cherif also traveled to Yemen for a short trip in 2011.
A U.S. official told CNN they are still corroborating information that Cherif also went to Yemen, but they have no reason to doubt the French government. Pelletier's sources said Cherif's wife told French authorities after the Paris attack that her husband traveled to Oman together with Said in the summer of 2011, but French security services have yet not been able to confirm the brothers made the trip together.
Pelletier's sources said that Cherif Kouachi was already under some form of control order in France at the time. He had previously served a prison sentence, after being convicted of terror offenses in 2008 for being part of a recruitment network for al Qaeda in Iraq. But the control order had been placed on him after he was implicated in a plot to break an Algerian terrorist from prison. Pelletier said it was not clear what type of control order he was under. Some require the surrender of passports, while others require regularly reporting to designated officials.
Morten Storm, a former jihadist who became a double agent working for Western intelligence services, told CNN that training trips such as Kouachi's were a regular part of operations for al Qaeda in the Arabian Peninsula when the terror group's external operations head was al-Awlaki, an American imam. Recruits were told to return home and avoid any appearance of radicalization.
"And that is what Anwar al-Awlaki had asked me for in the past to get brothers, i.e., Muslim terrorists, to get them over," Storm told Robertson. "But the condition was that they had to have a clean passport and they had to have a clean name. They do not have to be under any sort of radars or surveillance or interest by the government. So, they had to be totally clean from that."
Al-Awlaki was killed by a U.S. drone strike on September 30, 2011.