Usama bin Laden’s son-in-law was found guilty of conspiring to kill Americans. Sulaiman Abu Ghayth was convicted in a New York City court on Wednesday morning.

He was captured last year in Jordan and put on trial about three weeks ago on terror related charges.

Ghayth served as Al Qaeda’s spokesman after September 11 attacks. Prosecutors say he made a series of propaganda videos, including one in which he promised the “storm of airplanes will not abate.”

His lawyers argued that he was merely repeating words from bin Laden.

The jury deliberated for about six hours before reaching the guilty verdict on all three counts. Ghayth was also convicted of conspiracy, and providing material support and resources to terrorists.

He is the most senior Al Qaeda member to be tried in a civilian court.