The FBI thwarted an attempted terrorist bombing in Portland's Pioneer Courthouse Square before the city's annual tree-lighting Friday night, according to the U.S. Attorney's Office in Oregon.

A Corvallis man, thinking he was going to ignite a bomb, drove a van to the corner of the square at Southwest Yamhill Street and Sixth Avenue and attempted to detonate it.

However, the supposed explosive was a dummy that FBI operatives supplied to him,

signed Friday night by U.S. Magistrate Judge John V. Acosta.

, 19, a Somali-born U.S. citizen, was arrested at 5:42 p.m., 18 minutes before the tree lighting was to occur, on an accusation of attempting to use a weapon of mass destruction. The felony charge carries a maximum sentence of life in prison and a $250,000 fine.

The arrest was the culmination of a long-term undercover operation, during which Mohamud had been monitored for months as his alleged bomb plot developed.

"The device was in fact inert, and the public was never in danger," according to a news release from the U.S. Attorney's Office.

The investigation involved the FBI, Oregon State Police, Portland Police Bureau, Corvallis Police Department and Lincoln County Sheriff's Office.

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."

According to the FBI affidavit, the case began in August 2009 when Mohamud was in e-mail contact with an unindicted associate overseas who was believed to be involved in terrorist activities. In December 2009, while the unindicted associate was in a frontier province of Pakistan, Mohamud and the associate discussed the possibility of Mohamud traveling to Pakistan to participate in violent jihad.

The associate allegedly referred Mohamud to a second associate overseas and provided him with a name and e-mail address. In the months that followed, Mohamud made several unsuccessful attempts to contact the second associate.

Ultimately, an FBI undercover operative contacted Mohamud in a June 2010 e-mail under the guise of being an associate of the first unindicted associate.

Steve Duin

Mohamud and the FBI operative agreed to meet in Portland a month later. Mohamud allegedly told the FBI operative that he had written articles that were published in Jihad Recollections, an online magazine that advocated holy war.

Mohamud also indicated he intended to become "operational," meaning he wanted to put an explosion together but needed help. The two met again in August 2010 in a Portland hotel.

"During this meeting, Mohamud explained how he had been thinking of committing some form of violent jihad since the age of 15," the affidavit says. "Mohamud then told (the FBI operatives) that he had identified a potential target for a bomb: the Christmas tree-lighting ceremony in Portland's Pioneer Courthouse Square on Nov. 26, 2010."

The FBI operatives cautioned Mohamud several times about the seriousness of his plan, noting that there would be many people, including children, at the event, and that Mohamud could abandon his plans at any time with no shame.

"You know there's going to be a lot of children there?" an FBI operative asked Mohamud. "You know there are gonna be a lot of children there?"

Mohamud allegedly responded he was looking for a "huge mass that will ... be attacked in their own element with their families celebrating the holidays."

Mohamud dismissed concerns about law enforcement, explaining that, " ... It's in Oregon; and Oregon, like, you know, nobody ever thinks about," according to the affidavit.

"The threat was very real," said Oregon's FBI Special Agent in Charge Arthur Balizan. "Our investigation shows that Mohamud was absolutely committed to carrying out an attack on a very grand scale. At the same time, I want to reassure the people of this community that, every turn, we denied him the ability to actually carry out the attack."

Mohamud maintained his interest in carrying out the attack and spent months working on logistics.

He allegedly identified a location to place the bomb and mailed bomb components to the FBI operatives, who he believed were assembling the device. He also mailed them passport photos so he could sneak out of the country after the attack, according to the affidavit.

He provided the FBI operatives with a thumbdrive that contained detailed directions to the bomb location and operational instructions for the attack.

On Nov. 4, Mohamud and the FBI operatives traveled to a remote spot in Lincoln County, where they detonated a bomb concealed in a backpack as a trial run for the upcoming attack.

On the drive back to Corvalis, FBI operatives quizzed Mohamud about whether he was capable of looking at the bodies of those who would be killed in his planned Portland attack.

"I want whoever is attending that event to leave, to leave either dead or injured," Mohamud reportedly told the FBI operatives, the affidavit says.

Later that day, Mohamud recorded a video of himself with the FBI operatives in which he read a written statement offering his reasons for the planned Portland bombing.

On Nov. 18, FBI operatives picked up Mohamud to travel to Portland, where they would finalize details of the attack.

David S. Kris, assistant U.S. attorney general for national security, said, "The complaint alleges that Mohamud attempted to detonate what he believes to be a vehicle bomb at a crowded holiday event in downtown Portland, but a coordinated undercover law enforcement action was able to thwart his efforts and ensure no one was harmed. "

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