Story highlights Colorado school gunman Karl Pierson liked debate and cross-country running

But he alienated peers with talk about communism and winning every argument

"He was pretty geeky and nerdy, but in a charming way," friend says

One neighbor describes him as bright but a social misfit whose peers ridiculed him

To many of his neighbors, Colorado school gunman Karl Pierson was the wholesome boy next door who liked achievement and ran on the cross country team. He even worked on an Eagle Scout project two years ago.

To schoolmates, Pierson was known for his outspoken intelligence that served him well on the debate team. But at times, he acted "weird" and alienated peers with rants about communism and his aggressiveness to win every argument, they said.

One neighbor described him as bright but a social misfit whose peers ridiculed him. His mother had transferred him from another high school because of the mockery and altercations, the neighbor said.

Pierson, 18, opened fire Friday inside Arapahoe High School, where he was a senior. Claire Davis, 17, was wounded in a point-blank shooting, and Pierson, who apparently didn't know Davis, then killed himself in the library, Arapahoe County Sheriff Grayson Robinson told reporters Friday.

"He was a really smart kid. He was intelligent. He knew how to speak; he really did. I don't think I ever won an argument with that kid," junior Daylon Stutz said in the school parking lot on Saturday, when students were allowed to retrieve their cars.

Photos: Arapahoe High School shooting Photos: Arapahoe High School shooting Arapahoe High School shooting – Claire Davis, a 17-year-old senior at Arapahoe High School, died Saturday, December 21, eight days after she was shot by a student with a shotgun at the school in Centennial, Colorado. "Despite the best efforts of our physicians and nursing staff, and Claire's fighting spirit, her injuries were too severe," Littleton Adventist Hospital said in a statement. Hide Caption 1 of 18 Photos: Arapahoe High School shooting Arapahoe High School shooting – Arapahoe County Sheriff Grayson Robinson holds a picture of Davis at a press conference on Saturday, December 14, after identifying her as the victim of the shooting at Arapahoe High School the day before. Hide Caption 2 of 18 Photos: Arapahoe High School shooting Arapahoe High School shooting – Robinson identified the shooter as 18-year-old Karl Halverson Pierson, who killed himself after opening fire. Pierson had asked about a specific teacher when he entered the school armed with a shotgun on December 13. Hide Caption 3 of 18 Photos: Arapahoe High School shooting Arapahoe High School shooting – Students are escorted out of Arapahoe High School in Centennial, Colorado, on December 13. Hide Caption 4 of 18 Photos: Arapahoe High School shooting Arapahoe High School shooting – Students wait outside Arapahoe High school after being evacuated on December 13. Hide Caption 5 of 18 Photos: Arapahoe High School shooting Arapahoe High School shooting – Officers escort students out of Arapahoe High School. Hide Caption 6 of 18 Photos: Arapahoe High School shooting Arapahoe High School shooting – Susie Ohle hugs Rob Escue as he came out of the school on Friday afternoon. Hide Caption 7 of 18 Photos: Arapahoe High School shooting Arapahoe High School shooting – Ruben Allen hugs his son Alex Allen, 17, after being evacuated from the school Hide Caption 8 of 18 Photos: Arapahoe High School shooting Arapahoe High School shooting – Students and parents walk away from the school. Hide Caption 9 of 18 Photos: Arapahoe High School shooting Arapahoe High School shooting – Law enforcement personnel arrive at the high school in a military-style vehicle. Hide Caption 10 of 18 Photos: Arapahoe High School shooting Arapahoe High School shooting – SaSha Meiler is overcome with emotion after hearing the voice of her younger sister, a freshman. Hide Caption 11 of 18 Photos: Arapahoe High School shooting Arapahoe High School shooting – Parents Cathy Thorson, left, and Heather Moran, facing the camera, embrace while they wait for news on their children. Hide Caption 12 of 18 Photos: Arapahoe High School shooting Arapahoe High School shooting – Students walk away from the school in single file with their hands up. Hide Caption 13 of 18 Photos: Arapahoe High School shooting Arapahoe High School shooting – Students from Arapahoe High School gather at the school's track. Hide Caption 14 of 18 Photos: Arapahoe High School shooting Arapahoe High School shooting – People gather outside the school. Hide Caption 15 of 18 Photos: Arapahoe High School shooting Arapahoe High School shooting – Parents wait for word about their children after a gunman opened fire at the school. Hide Caption 16 of 18 Photos: Arapahoe High School shooting Arapahoe High School shooting – Members of law enforcement are seen outside the school. Hide Caption 17 of 18 Photos: Arapahoe High School shooting Arapahoe High School shooting – Law enforcement personnel gather near the high school. Hide Caption 18 of 18

Stutz, an offensive tackle on the football team, had known Pierson since the two shared a human behavior class when Stutz was a freshman and Pierson a sophomore. They worked on a class experiment together in which they went into the community and tried breaking unwritten rules, Stutz said.

"I did think he was a little weird, but I didn't think he was, like, bad weird," Stutz added. "He always kind of talked about how America was a communist country, how the government was, like, trying to take us over and stuff. I don't know, just some weird stuff that I didn't really pay close attention to, but nothing that alarmed me.

"He was definitely kind to me. I never saw him mean to anybody. He wasn't condescending to anyone," he said.

In Friday's shooting, Pierson was armed with a shotgun, a bandolier stocked with ammunition, a machete and three Molotov cocktails, Robinson said. Pierson fired five shots within 1 minute and 20 seconds, he said.

was apparently seeking revenge against a faculty member because of a "confrontation or disagreement," the sheriff said. Pierson entered his school looking for the debate team's coach, CNN affiliate KUSA reported, citing Robinson. Piersonwas apparently seeking revenge against a faculty member because of a "confrontation or disagreement," the sheriff said.

High school senior Frank Woronoff said he had known Pierson since they were freshmen.

"He was the last person I would expect to shoot up a high school," Woronoff said.

"He was pretty geeky and nerdy but in a charming way, one of the nicest, most humble people I know," he added.

Senior Chris Davis, 18, was among many students Saturday trying to make sense of Pierson's shooting rampage.

"He was a weird kid," Davis said. "He's a self-proclaimed communist, just wears Soviet shirts all the time."

Pierson became easily aggravated, "always liked to be right" and didn't like losing, Davis said.

"It seems realistic, now, that he did it," Davis added.

The home where authorities believe Pierson armed himself is five miles from his school and appeared vacant Saturday. Its front door was sealed and boarded a day after federal agents raided the property and executed search warrants.

A man who declined to be identified in an CNN interview lives a few doors away and said he has known Pierson since he was a boy. In the last few days, the neighbor noticed Pierson driving at excessive speeds throughout their normally quiet, modest middle-class suburb.

The neighbor said Pierson's mother, Barbara, transferred her son to Arapahoe High School from nearby Highland Ranch High School because her son had been subjected to constant ridicule and physical altercations.

"He was socially awkward and just didn't seem to fit into the larger teenage groups, and I think that weighed on him," the neighbor told CNN.

The neighbor said Pierson's parents had been separated for years, and Karl was living with his mother and younger sister.

"While Karl was socially a misfit around kids his age, he was intellectually bright and loved to debate in school," the neighbor said. "If he was disciplined in a debate class, that must have meant everything to him. It may have been trigger point."

Pierson was active in his community, KUSA reported.

He took pride in how he routinely won contests on his speech and debate team, the station reported. He showed off his first place and second place trophies online.

One neighbor described him as a "nice young man," the affiliate said.

In fact, the TV outlet interviewed him seven years ago about the design of a quarter commemorating Colorado.

Pierson submitted questions to the station in 2008 for a show about the Colorado Supreme Court and asked a question at a U.S. Senate debate in 2010, the news outlet said.