(CNN) -- News that Mohamed Osman Mohamud was arrested as a suspected terrorist came as a shock to the woman who lived across the street from him and his family until about a year ago.
Stephanie Napier played cards with Mohamud's mother, Myriam, and Mohamud's sister, Mona, walked Napier's youngest son to school. Napier's son Tyler played basketball with the 19-year-old accused of planning to detonate a vehicle bomb outside a Christmas-tree-lighting ceremony in Portland, Oregon.
Napier said Monday that Mohamud was a "quiet kid" who came from a "normal middle-class family," not the man a federal grand jury now has charged with plotting to blow up the Friday night ceremony.
"I think that's why it's so shocking," said Napier, whose son woke her up in the middle of the night with news of her former neighbor's arrest. The news came just hours after her husband, a staff sergeant with the Army Reserve, left on his second tour of duty in the Middle East.
Mohamud, a naturalized U.S. citizen from Somalia, pleaded not guilty Monday to a single count of attempting to use a weapon of mass destruction. A federal grand jury in Portland indicted him on that charge shortly before his Monday afternoon court appearance, and he could face life in prison if convicted.
About 100 people, including several members of the area's Somali-American community, packed the small hearing room and the hallway outside. Mohamud did not acknowledge them during the hearing.
The Oregon State University student was arrested Friday after he attempted to detonate what he believed was an explosives-laden van parked near a tree-lighting ceremony in Portland's Pioneer Courthouse Square, law enforcement officials said. But the bomb was fake, thanks to an undercover operation designed to undermine the plotter, and officials said the public was never in danger from the mock device.
Mohamud's lawyer, Stephen Sady, said government agents entrapped his client into the plot, "grooming" him as a potential bomber and providing him with money and transportation to support the plot.
"The government used the complaint as a press release, timed for maximum publicity and impact," Sady said.
The Justice Department has said Mohamud's arrest came after a long-term undercover operation during, which the teen had been monitored closely. Dwight Holton, the U.S. attorney in Portland, said Mohamud's own actions dictated the timing of his arrest and "led him here today."
"It's what the defendant did that created the timing," Holton said.
U.S. Magistrate John Acosta set a February 1 trial date for the suspect, who wore a light-colored shirt, dark-blue pants an shackles during his brief appearance Monday. No bail has been set.
Napier said that neither she nor her son ever "heard anything negative or derogatory" from Mohamud. He could be "just a messed-up kid, you know, who made a bad decision," Napier added.
But Arthur Balizan, the FBI special agent in charge in Oregon, called the threat posed by the reported plot "very real."
"Our investigation shows that Mohamud was absolutely committed to carrying out an attack on a very grand scale," Balizan said. "At the same time, I want to reassure the people of this community that, at every turn, we denied him the ability to actually carry out the attack."
According to an arrest warrant affidavit by an FBI special agent, Mohamud was in e-mail communication in August 2009, with a person believed to be involved in terrorist activities. In December, that person was "located in the northwest frontier province of Pakistan," the affidavit states.
The two communicated regularly, the affidavit states, and "using coded language, they discussed the possibility of Mohamud traveling to Pakistan to prepare for violent jihad."
Mohamud attempted to contact another associate who he thought would help facilitate his travel overseas, the affidavit states, but "because Mohamud used the wrong e-mail address in his efforts to contact [the second associate], he never successfully contacted him to arrange travel."
An undercover FBI employee contacted Mohamud in June under the guise of being affiliated with the associate in Pakistan, according to the affidavit. Mohamud met with the undercover operative July 30 in Portland. Mohamud allegedly told the undercover operative that he had written articles published in Jihad Recollections, an online magazine that advocated violent jihad.
"Mohamud also indicated that he wanted to become 'operational,' " the Justice Department said. "Asked what he meant by 'operational,' Mohamud stated that he wanted to put an 'explosion' together, but needed help."
But Sady noted that government agents failed to record their first contact with Mohamud due to what the affidavit said were technical difficulties, questioning why a meeting so critical to the case wasn't captured on video or audiotape.
At a meeting in August, the Justice Department said, Mohamud told undercover FBI operatives that he had been thinking of committing violent jihad since the age of 15. According to the affidavit, Mohamud then told undercover operatives that he had identified a potential target for a bomb: the annual Pioneer Courthouse Square tree-lighting.
Authorities said an FBI operative pointed out that lots of children would be at such an event, but Mohamud said he was looking for a "huge mass that will ... be attacked in their own element with their families celebrating the holidays." Officials said Mohamud also stated, "It's in Oregon, and Oregon like, you know, nobody ever thinks about it."
According to the affidavit, Mohamud and the undercover FBI operatives went to a remote area in Lincoln County, Oregon, on November 4 and detonated a bomb hidden in a backpack as a test. During the drive back to Corvallis, the agents asked Mohamud whether he could look at the bodies of those who would be killed in the upcoming attack in Portland, the Justice Department said.
Mohamud said, "I want whoever is attending that event to leave, to leave either dead or injured," according to the affidavit.
On Friday, Mohamud met one of the FBI operatives at a predetermined location, the affidavit states. Mohamud called a phone number "in an unsuccessful attempt to detonate the device," it says, and then dialed the number again before he was taken into custody.
Portland police Sgt. Pete Simpson, who said police officers got involved in the investigation several months ago, said the arrest took place several blocks from the tree-lighting.
Muslims in the Portland area have decried the alleged plot and thanked police for reaching out to mosques in the area. And Somali leaders in neighboring Washington state also condemned the alleged plot, calling it "heinous" in a statement issued Monday.
CNN's Thelma Gutierrez and Paul Vercammen contributed to this report.