Federal agents thwarted an attempt to explode a car bomb during a Christmas tree lighting ceremony in Portland’s Pioneer Courthouse Square, Friday. A Somali-born teenager was provided ‘fake explosives’ in a sting operation begun last summer.

U.S. Attorney Dwight Holton released federal court documents Friday that show the sting operation began in June after an undercover agent learned that Mohamud had been in contact with an “unindicted associate” in Pakistan’s Northwest Frontier region.

Mohamud is a naturalized U.S. citizen who has been living in Corvallis.

According to a federal complaint, Mohamud was in regular email contact with the “unindicted associate’ in Pakistan’s Northwest Frontier starting in August 2009.

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Mohamud will appear in U.S. District Court in Portland on Monday.

“This defendant’s chilling determination is a stark reminder that there are people — even here in Oregon — who are determined to kill Americans,” said Oregon U.S. Attorney Dwight Holton. “The good work of law enforcement protected Oregonians in this case — and we have no reason to believe there is any continuing threat arising from this case.”