The two brothers wanted in the terror attack on a French weekly that killed 12 people Wednesday had long been viewed by U.S. officials as potential terror suspects, prompting them to be placed on a “no fly” list that banned them from boarding commercial aircraft into and out of the United States, U.S. counterterrorism sources told Yahoo News.

Cherif Kouachi, 32, and his brother, Said, 34, had both been entered into the U.S. government’s Terrorist Identities Datamart Environment (TIDE) system — a classified master database with more than 1 million names of individuals suspected of possible terror ties.

But the sources said information about the Kouachis was viewed as serious enough for their names to be forwarded to the FBI’s Terrorist Screening Center for entry onto a number of government watch lists. The Kouachis were then placed on the “no fly” list — the most restrictive of the lists, with about 47,000 names.

A person placed on that list is viewed as a “threat to civil aviation or national security,” a U.S. official said. The official declined to say precisely when the Kouachis were placed on the list other than that they had been on it “for years.”

U.S. officials also declined Thursday to say what information prompted the watch-listing. But, according to press reports, Cherif Kouachi came to the attention of French authorities as early as 2005 when he was arrested in connection with a case involving Farid Benyettou, a radical preacher who gave sermons calling for jihad in Iraq.

Kouachi was brought to trial in 2008; according to trial testimony, he had become radicalized by the U.S. invasion of Iraq and the later images of detainee mistreatment in Abu Ghraib prison. He was convicted and given a three-year sentence for being involved in a network that recruited young French Muslims to fight in Iraq, but was then released because of the time he spent in pretrial detention.