The Pentagon confirmed on Thursday that a terrorist linked to the September 11, 2001, attacks on the United States was captured in Syria by U.S.-backed forces more than a month ago, Reuters reported.

The Syrian Democratic Forces (SDF), a coalition of Arab and Kurdish fighters, said on Wednesday it had captured Syrian-born German national Mohammed Haydar Zammar, who was accused of helping to plan the attacks.

“We can confirm that Mohammad Haydar Zammar, a Syrian-born German national, was captured more than a month ago by SDF partners as part of their ongoing operations to defeat ISIS inside Syria,” Pentagon spokesman Eric Pahon said, using an acronym for Islamic State.

The Pentagon had initially said it could not confirm the report of Zammar’s capture.

“We are working with our SDF partners to obtain additional details,” Pahon added, according to Reuters.

The 9/11 Commission report, a Congressional account on the 2001 attacks, said Zammar was an “outspoken, flamboyant Islamist” who extolled “the virtues of violent jihad.”

It said Zammar reportedly had taken credit for influencing Ramzi Binalshibh, who is accused of wiring money to September 11 hijackers and passing information to Al-Qaeda operatives, and Mohammed Atta, who led the attack on the World Trade Center in New York City.

Zammar, who is in his mid-fifties, was detained in Morocco in December 2001 in an operation involving CIA agents, and was handed over to the Syrian authorities two weeks later.

A Syrian court sentenced Zammar to 12 years in prison in 2007 for belonging to the Muslim Brotherhood, a charge that at the time could have resulted in the death penalty.

Due to the civil war in Syria, many hardline Islamist prisoners have either been released from jail or broke free and went on to join jihadist groups fighting in the war.

Al-Qaeda in the past operated a branch in Syria known as the Al-Nusra Front. However, the two groups cut ties in late July of 2017. The group now goes by the name Fateh al-Sham and is designated a "foreign terrorist organization" by the U.S.