The younger of the two brothers who carried out the terrorist attacks in Paris - not the older, as initially believed - was the aggressor, U.S. counter terrorism officials revealed on Wednesday.

American investigators said Chérif Kouachi could have received training and $20,000 from Al Qaeda in Yemen when he traveled there in 2011 most likely using the passport of his older brother, Saïd. The money was presumably meant to fund attacks when he went back home to France.

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In a written and video message, Al Qaeda's affiliate in Yemen has formally claimed responsibility for staging the string of attacks in France. The message said the Al Qaeda leadership picked the target but did not mention their names.

French and American investigators have been digging deeper into the background of the Kouachi brothers to determine who was exactly behind the attack on the satirical publication Charlie Hebdo, and the participation, if indeed there was, of Al Qaeda or its affiliates.

If Al Qaeda in Yemen's claim of responsibility was proven, the attacks in France could be the deadliest offensive funded and orchestrated by Al Qaeda against a Western country since the 2005 transport bombings in Britain that left 52 people dead.

The American authorities now believe Chérif most likely had contact with an American-born cleric, Anwar al-Awlaki in Yemen, most likely in person. al-Awlaki reportedly had a hand in attacks against Western nations by AQAP or Al Qaeda in the Arabian Peninsula.

Brian Fishman, a counter terrorism researcher at the New America Foundation, suspected that Chérif did engage AQAP in Yemen, but that the organization has not granted him full membership. Fishman said that concerns over infiltration by Western agents may have prompted AQAP to offer only basic training, ordered recruits to carry out attacks against already disclosed targets and sent him back to France.

He said that if that was the case, AQAP fell short of directing the attack, but it did have some control of the Kouachis and it could, by extension, do claim credit.

The message of Al Qaeda's affiliate in Yemen hailed the Kouachi brothers as Islam's two heroes. French military forces fatally gunned them down in a raid on Friday. 

TagsParis terror attack, Kouachi brothers