In the conservative southern Utah city where Tyler Robinson grew up, neighbors and classmates described him as a reserved, intelligent young man raised in a Republican family who was deeply interested in video games, comic books and current events.

On Friday afternoon, people who knew Mr. Robinson struggled to reconcile their memories of him and his seemingly ordinary suburban upbringing with his notorious new image: the latest face of political violence, accused of fatally shooting the conservative influencer Charlie Kirk on a Utah college campus earlier this week in what the authorities have called a political assassination.

“It’s really sad that someone with his mind put it to that sort of use,” said Keaton Brooksby, 22, a former high school classmate of Mr. Robinson’s.

Mr. Robinson had recently spoken with a family member about the fact that Mr. Kirk was going to hold an event in Utah, according to a police affidavit, and he and his relative discussed “why they didn’t like him and the viewpoints he had.”

But as elements of the nation’s political left and right scrambled for motives, the image that has initially emerged of Mr. Robinson is not at all clear. Neither is his trajectory from a scholarship-winning high school student to an apprentice electrician to a suspect.

Mr. Brooksby said that Mr. Robinson was generally considered a quiet pupil when they were growing up in the conservative St. George area, but one day in high school, the topic of the 2012 attacks on Americans in Benghazi, Libya, came up during lunch. Few there knew exactly what had happened, but Mr. Robinson was sure of himself.

“He gave us a whole spiel on what happened,” Mr. Brooksby said. “I just remember thinking, he’s got a lot of information on this for someone who’s 14.”

Mr. Robinson is registered to vote in Utah, but he is not affiliated with a political party and had never voted in an election, according to the Washington County Clerk. His parents are registered Republicans, both with active hunting licenses in a part of the country known for its outdoor life, near Zion and Bryce Canyon national parks.

Social media photos posted by his family over the years show Mr. Robinson and his two younger brothers shooting and posing with guns.

Mr. Robinson surrendered to the police near his hometown on Thursday night after an intense, 33-hour manhunt. A police officer wrote in an affidavit filed in court that one of Mr. Robinson’s family members had described him as growing “more political in recent years” and, during a recent dinner, had mentioned Mr. Kirk and his upcoming event at the Utah campus.

Officials said they found, left with the gun, unfired ammunition that had been engraved with jokes and slang from internet memes as well as the words, “hey fascist! CATCH!”

Adrian Rivera, 22, who had been in a high school woodworking class with him, said that Mr. Robinson would often hang around the area designated for the Junior R.O.T.C., or Junior Reserve Officers Training Corps, with other students who were interested in the military program. It was unclear whether Mr. Robinson had actually been a member of the corps.

Mr. Rivera said that Mr. Robinson was a “massive Halo guy,” referring to the popular science fiction game, and that he also liked to play Call of Duty, and other shooter games.

Mr. Robinson appeared to excel academically as a teenager. His mother posted online a photo of him when he graduated from middle school with a perfect 4.0 grade point average. In a Facebook post from August 2020, celebrating the start of Mr. Robinson’s senior year at Pine View High School in St. George, his mother proudly reported that he had been taking four college-level classes as well as Advanced Placement calculus. He graduated from Pine View in 2021.

“My brain hurts for him, but he’s so excited!” she wrote in the post.

Jaida Funk, 22, who went to elementary and middle school with Mr. Robinson, said he was an excellent student — they were both in high honor roll together. In fact, she said, he had the personality of a teacher’s pet, always on time, respectful, hardworking, and smart.

“He’s the kind of kid that even if you are not friends, you’d ask him to be in your group project,” she said. “He’s someone you’d expect to get the award for perfect attendance.”

She said he was very into computers. He was not in the popular crowd but people liked him.

“The way he carries himself and speaks to others. I thought he’d be a CEO or a businessman. He had good leadership qualities.”

In 2021, Mr. Robinson’s mother posted a video of her son reading a letter in which he said he had received a presidential scholarship to Utah State University worth $32,000. But a university spokeswoman said that Mr. Robinson only attended the university for one semester in 2021, as a pre-engineering major. The school is roughly two hours away from Utah Valley University, where the shooting took place.

At the time of the shooting, Mr. Robinson appears to have been living with at least one roommate in an apartment complex in St. George, about a 10-minute drive from his family’s home in the adjoining town of Washington, Utah. The police said that they had interviewed a roommate of Mr. Robinson’s, who showed them messages from after the shooting in which Mr. Robinson described leaving a rifle somewhere and changing his clothes.

Mr. Robinson had been a third-year student in an electrical apprentice program at Dixie Technical College in St. George, the school said in a statement.

Several of Mr. Robinson’s neighbors at the apartment complex where he had recently lived described him as withdrawn, saying that they rarely saw him, apart from when he was walking to and from a gray Dodge Charger he kept in the parking lot.

“He’d never talk to anybody,” said Josh Kemp, 18, who lived across from Mr. Robinson’s apartment. “He’d always blast music with his roommate.”

Oliver Holt, an 11-year-old who lives a few doors down from Mr. Robinson’s apartment, said he was going door-to-door in the complex last week, asking neighbors whether he could do any odd jobs to help him save up for a new phone, when he encountered Mr. Robinson. Oliver said he was put off by Mr. Robinson’s behavior, and said he kept glancing back into his apartment.

“He was acting pretty strange,” Oliver said. “He was acting kind of nervous and scared.”

Mr. Brooksby, who knew Mr. Robinson in high school, said the last time he saw Mr. Robinson was when they bumped into each other at a Walmart. Mr. Robinson seemed to have grown even shyer, appearing to not want to catch up.

Kirsten Noyes contributed research.