Osama bin Laden’s son-in-law was convicted of aiding al-Qaida after the Sept. 11, 2001, attacks by helping bring in new terrorist recruits and acting as a spokesman for the group in a series of fiery speeches broadcast around the globe.

A federal jury in Manhattan today found Sulaiman Abu Ghayth guilty of charges that he conspired to kill U.S. nationals and provided material support to a terrorist group. Jurors reached their verdict following a three-week trial in a courthouse just blocks from where World Trade Center once stood. The conspiracy to kill charge carries a maximum sentence of life in prison.

Abu Ghayth, 48, the most senior al-Qaida member to be tried in a U.S. civilian court since the terrorist attacks, was captured by American agents after a decade-long manhunt and is regarded as among the group’s most influential surviving leaders after Navy SEALs killed bin Laden in May 2011.

The case was the highest-profile terrorism trial in New York City since the Obama administration in 2011 abandoned its plan to hold a civilian trial there for Khalid Sheikh Mohammed, the self-proclaimed mastermind of the Sept. 11 attacks, and instead ordered him to face a military tribunal in Guantanamo Bay, Cuba. For security, the identities of jurors weren’t disclosed in court and they were escorted to and from the building by U.S. Marshals throughout the trial.

Abu Ghayth was portrayed by prosecutors as an “essential” member of al-Qaida in his role as a spokesman for the group in numerous videos made in the wake of the attacks. The government also alleged he had advance knowledge of other plots, including a foiled scheme to detonate shoe bombs on passenger jets that included convicted terrorist Richard Reid.

Abu Ghayth, an Islamic cleric originally from Kuwait, testified in his own defense that he didn’t play any role in terrorist plots. He insisted the when he preached to recruits at an al-Qaida training camp in 2001 at bin Laden’s request, he urged them to have “merciful hearts.” His lawyers claimed the government didn’t prove that he was involved in planning the Sept. 11 attacks or knew of the shoe-bomb plot.