Published: Nov 28, 2010 9:18 PM EST
Updated: Nov 28, 2010 6:18 PM EST

PORTLAND, Ore. (AP) - FBI documents detail conversations between Mohamed Osman Mohamud and undercover agents, in which the Somali-born teen describes Pioneer Courthouse Square in Portland, Ore., as the perfect location to set off a car bomb, because it would be packed with "families celebrating the holidays" during Friday's Christmas tree lighting ceremony.
      
But authorities have not come up with an explanation for how Mohamud became so radicalized. Officials say he had no formal ties to foreign terror groups, though he had tried to contact suspected terrorists in Pakistan.
      
Oregon State University says Mohamud dropped out of the school in early October and had not declared a major. The imam at the Islamic center in Corvallis describes Mohamud as a normal student who went to sports events, occasionally drank a beer and liked rap music. The imam says Mohamud was religious but didn't come to the mosque consistently.
      
But Mohamud told undercover agents that at age 15, he had prayed for guidance about whether he should "make jihad in a different country" or in the U.S.

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