Sinh Vinh Ngo Nguyen pleaded guilty to one count of attempting to provide material support to a designated foreign terrorist organization.
The 24-year-old was arrested in Santa Ana on Oct. 11 as he was waiting to board a bus to Mexico.
Nguyen, who also used the name Hasan Abu Omar Ghannoum, admitted in a plea agreement that he went to Syria about a year ago and joined opposition forces. He told people through social media that he was fighting the Assad regime, and when he returned to the U.S., Nguyen offered to train al Qaeda forces in Syria, but his offer was turned down.
Federal authorities say Nguyen met with an undercover FBI agent who he believed was an al Qaeda recruiter between Aug. 3 and Oct. 11. He told the man he wanted to return to jihad because "this was what he was born to do."
Nguyen gave the FBI agent a photo of himself and a passport application with "bogus information," investigators said, and he agreed to train 30 al Qaeda fighters in Pakistan.
In the plea agreement, Nguyen admitted that on Oct. 1, he purchased a plane ticket to travel from Mexico to Peshawar, Pakistan. When he was taken into custody, Nguyen had a fraudulent passport and a computer hard drive that had "over 180 training videos on shooting firearms," investigators said.
Nguyen faces a statutory maximum penalty of 15 years in federal prison when he is sentenced on March 21, 2014.