Sulaiman Abu Ghaith, a son-in-law of Osama bin Laden, has been convicted in Manhattan for conspiring to kill Americans. He is the most senior advisor to the Al Qaeda leader to be tried in American civilian court in connection with the Sept. 11, 2001 attacks.

Abu Ghaith, a Kuwaiti-born cleric married t0 Bin Laden’s daughter Fatima, was captured in Jordan in March 2013 and pleaded not guilty. The trial began earlier this month. According to NBC News, a federal jury took five hours to deliberate before finally finding Abu Ghaith guilty. He will be sentenced on Sept. 8 and faces life in prison.

During the trial, Abu Ghaith did take the stand, although he wasn’t expected to, notes The New York Times. He told the jury how he had met with Bin Laden in a cave the night after the Sept. 11 attacks. Bin Laden told Abu Ghaith a day later that he needed him to help “deliver a message to the world.”

Prosecutors also showed videos in which Abu Ghaith praised the Sept. 11 hijackers. He also warned about more attacks in an October 2001 video.

Abu Ghaith, 48, was also convicted of providing material support to terrorists and conspiracy to provide material for terrorists. The charges come with maximum sentences of 15 years in prison for each.