"The FBI monitored Mohamud's e-mail and found that he was in contact with people overseas, asking how he could travel to Pakistan and join the fight for jihad, according to an FBI affidavit.

According to the law enforcement official, Mohamud e-mailed a friend living in Pakistan who had been a student in Oregon in 2007-2008 and been in Yemen as well."
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He may have acted alone but he gained assistance from undercover agents posing as someone other than F B I agents. Got his inspiration from insurgent groups. Talked to people in foriegn countries about joining the terror groups.
Acting alone and getting inspiration from terrorist makes him a terrorist. He will probably be tried as a non terrorist by the looks of the story.