By Eliott C. McLaughlin and Carolyn Sung

CNN

WYOMING, Ohio (CNN) -- The Ohio hometown of Otto Warmbier, who died last week after his return from 17 months in detention in North Korea, gathered at the 22-year-old's alma mater Thursday to bid him farewell.

Around 2,500 somber well-wishers waited in two lines outside Wyoming High School's arts center for his funeral, which lasted roughly 45 minutes. The auditorium in this Cincinnati suburb can hold just 800 people, so most attendees watched the service on monitors in overflow rooms.

Inside the arts center, mourners were met with a display of belongings Warmbier took with him on what was supposed to be a five-day excursion to North Korea. They included his wallet, running and boat shoes, a University of Virginia notebook, a scientific calculator, a reusable grocery bag and the crumpled linen blazer he wore while there.

The school's parking lot was also packed, and nearby streets were blocked to provide parking for attendees and the media.

Among the speakers at the funeral were Warmbier's brother, Austin, his sister, Greta, and some of his friends, according to the funeral program. Also in attendance was US Ambassador Joseph Yun, the special representative for North Korea policy, who helped secure Warmbier's release.

The front of the funeral program featured a quote from Warmbier's 2013 salutatorian speech: "This is our season finale. This is the end of one great show, but just the beginning to hundreds of new spinoffs."

After the speakers concluded, a police officer from the nearby suburb of Mariemont played the bagpipes as he led the casket, followed by a long line of mourners, out to a waiting hearse.

'The nicest kid'

Funeral organizers asked supporters to line the 3-mile trek between the school and the cemetery where Warmbier will be laid to rest. On campus and around the school, ribbons of blue and white -- Wyoming High School's colors -- adorned trees to honor Warmbier.

Andrew Kraner, 25, who knew Warmbier from school and swimming "up the hill at the YMCA," said the funeral featured a blend of serious and lighthearted moments -- which "really spoke to Otto's character." Despite the uplifting celebration of his classmate's life, Kraner lamented "a very bright future that we'll never know."

"Everything they say about Otto is very true. He was the nicest kid," he said. "It's tough, and my heart's very heavy for him."

Kraner had trouble finding the words to describe his reaction to learning that a friend from this tight-knit community of 8,400 people had lost his life amid such a public, international ordeal.

That sentiment was echoed by Cynthia Meis, who became Wyoming High's director of college counseling ahead of Warmbier's senior year. She recalled the community "holding our breaths, praying for a quick release, rallying around the Warmbiers as much as possible" amid a dearth of information about the former student's fate.

Compounding their remorse was the stellar nature of Warmbier's character, she said, explaining he possessed a rare combination of intelligence, affability and sincerity.

"He was going to set the world on fire, which is why this loss is so profound," she told CNN.

Parents: This is a celebration

Warmbier returned to the United States last week in a coma, only to die six days after his arrival. North Korean officials say Warmbier contracted botulism and slipped into a coma after taking a sleeping pill.

His official cause of death is unknown, as his parents declined to have an autopsy conducted on their son.

"It would be easy at a moment like this to focus on all that we lost -- future time that won't be spent with a warm, engaging, brilliant young man whose curiosity and enthusiasm for life knew no bounds," Fred and Cindy Warmbier said in a statement.

"We choose to focus on the time we were given to be with this remarkable person. You can tell from the outpouring of emotion from the communities that he touched -- Wyoming, Ohio, and the University of Virginia to name just two -- that the love for Otto went well beyond his immediate family."

Attendee D'Shon Shapiro told CNN that she and a friend, Molly Cain, know Warmbier's parents from youth sports. Otto Warmbier coached Cain's son in swimming and "made a great impression on him," she said.

"They truly are remarkable people, having raised remarkable kids," Shapiro said of Warmbier's parents.

Shapiro and Cain set up a fund-raiser on Facebook for the Warmbiers, with hopes of raising enough money to buy a memorial bench and to plant a tree at the young man's alma mater.

"With $10,500 raised so far, we're out of our element," Shapiro said. "What we insist on, though, is that Fred and Cindy make the decision on how to use the funds to best memorialize Otto."

Mysterious death

Warmbier visited North Korea in January 2016 on a sightseeing tour. He was arrested for allegedly stealing a political sign from a restricted area and sentenced two months later to 15 years of hard labor.

President Donald Trump's administration worked to secure his return, and upon doing so, learned Warmbier could not speak or move voluntarily. His doctors said he suffered extensive brain damage.

His physicians said he suffered from unresponsive wakefulness, a condition also known as persistent vegetative state. In a news conference before Warmbier's death, they said they found no evidence of botulism, casting doubt on North Korea's claim.

"This pattern of brain injury is usually seen as result of cardiopulmonary arrest where blood supply to the brain is inadequate for a period of time, resulting in the death of brain tissue," Dr. Daniel Kanter said last week.

'They are responsible'

Sen. Rob Portman, R-Ohio, in remarks to reporters before the funeral, said he and his wife had spent Warmbier's 22nd birthday in December with the detained young man's parents. He described Warmbier as outgoing, athletic, bright and curious.

The senator accused North Korea of a "disregard for basic human rights, basic human dignity." He said he suspected Warmbier was denied basic medical care while detained in the reclusive country.

"Yes, they are responsible," Portman said of the North Korean regime. "This college kid never should've been detained in the first place."

The Hamilton County Coroner's Office conducted only an external examination Warmbier's body. The coroner's office reviewed medical records from the University of Cincinnati Medical Center and the air ambulance service that helped ferry Warmbier from Pyongyang to Cincinnati.

"No conclusions about the cause and manner of Mr. Warmbier's death have been drawn at this time as there are additional medical records and imaging to review and people to interview," the coroner's office statement said.

CNN's Faith Karimi, Emanuella Grinberg, Miguel Marquez and Kelly Christ contributed to this report.