Charlie Hebdo massacre gunman reportedly knew underwear bomber

One of the brothers who carried out a massacre at the offices of the satirical French magazine Charlie Hebdo lived across the hall from the so-called "underwear bomber" while the two attended an Arabic-language school in Yemen in 2009, according to a published report.

The Wall Street Journal, citing neighbors of both men as well as Yemeni intelligence officials, reported that Said Kouachi and Umar Farouk Abdulmutallab studied together and often visited the mosque in the Old City of Yemen's capital, San'a.

However, a Yemeni official close to the investigation told Fox News that while the pair attended the same school, it did not appear they were friends or roommates.

This past Wednesday, Said Kouachi and his younger brother, Cherif, entered the Paris offices of the Charlie Hebdo magazine and killed twelve people, including eight of the magazine's staffers. Two days later, the brothers were killed by police who had surrounded them in a printing shop located in a small village about 25 miles northeast of Paris.

On Friday, U.S. government sources confirmed to Fox News that Said Kouachi had travelled to Yemen in 2011 and trained with or fought along side Al Qaeda in the Arabian Peninsula (AQAP), and one of his goals was to meet with the Al Qaeda branch's leadership, though it is not clear that he ever managed to do so. A U.S. intelligence assessment described to The Associated Press shows that Kouachi was trained in preparation to return home and carry out an attack.

The Journal reports that Kouachi arrived in Yemen in early 2009 on a student visa issued by the language school and was often seen with Abdulmutallab. However, Said began disappearing for long periods of time, sometimes as long as a week, for reasons neighbors said he described as "personal issues." U.S. officials say Kouachi's absences coincide with the period that Abdulmutallab had begun training with AQAP.

Abdulmutallab, a Nigerian national, attempted to blow up a jet plane over Detroit on Christmas Day, 2009. He failed to detonate the explosives on his body and was later arrested. He was convicted on terrorism charges in 2012.

The Journal reports that Said Kouachi remained in Yemen until at least mid-2010, but later returned near the end of that year, and stayed through most of 2011. It is not clear of Said's stay overlapped with that of his brother Cherif, who claimed to a French TV station before his death Friday that he was sent by AQAP and had been financed by the American-born cleric Anwar al-Awlaki, who was killed by a U.S. airstrike in Yemen in 2011.

The group has not issued a formal claim of responsibility for the Charlie Hebdo massacre, but a member of the group told the Associated Press Friday that a formal claim would be made in the coming days. Shortly after the Wednesday's attack, a series of tweets went out from a known AQAP Twitter account. They show images of the Paris massacre with photos of al-Awlaki and Samir Khan, the editor of Inspire magazine, who was killed along with al-Awlaki.

An intelligence source told Fox News that the tweets suggested foreknowledge of the Paris attack.

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Fox News' Catherine Herridge and The Associated Press contributed to this report.