By Mandi Bierly
Updated July 22, 2010 at 03:14 PM EDT

Zachary Adam Chesser, the 20-year-old U.S. citizen who posted online warnings to South Park creators Trey Parker and Matt Stone after the airing of their Mohammad-themed 200th episode, was arrested July 21 on charges of providing material support to an extremist group that has ties to al Qaeda, Reuters reports. According to the FBI, Chesser admitted that on July 10, when he was stopped from boarding a flight from New York to Uganda, he was on his way to Somalia to join the al Shabaab group, which U.S. officials believe has fought alongside al Qaeda in Afghanistan. Per Reuters’ report, Chesser also said he changed his mind about joining al Shabaab after it claimed responsibility for deadly bombings in Uganda earlier this month.