Tacoma Dome officials don’t know why a monster truck launched a Frisbee-sized hunk of metal into the stands Friday night, killing a 6-year-old boy.

An investigation is under way into the accident, which also injured an adult spectator, Tacoma deputy city manager Rey Arellano said Saturday.

City officials didn’t have enough information about the accident to describe it Saturday afternoon, and Monster Jam show producer Feld Motor Sports did not divulge details.

The missile-like debris struck Graham Elementary kindergartner Sebastian Hizey in the head, shearing off a 3-inch-long, 3-inch-wide chunk of his skull, said his father, Jessie Hizey of Puyallup.

Sebastian Hizey died early Saturday. No information was available on the man who was injured.

The accident occurred as a crowd of 10,000 watched Natural High, a huge red-and-silver truck, spinning doughnuts in the dirt. The behemoth vehicle, crippled and forklifted away earlier in the show, roared back onto the track following a break, Jessie Hizey said.

The crowd cheered as its massive churning tires spun up mud. Suddenly, a metal ring weighing 7 to 12 pounds rocketed out from under the truck into the east end of the stands, Jessie Hizey said.

The boy who loved cars and trucks and coloring books had been teasing his mom, tickling his friends and immersing himself in the noise and drama of the show.

“You go out for a night of fun, and you lose your son,” Hizey told The News Tribune Saturday afternoon, his voice a saddened whisper, his face contorted in grief.

At the family’s home, parents, family and friends consoled one another, fresh bursts of sobs passing from one to the other like electric shocks.

Sebastian “was a very funny kid, a very good kid,” his dad said.

When mom Phyllis Dwyer returned from the restroom during the truck rally Friday night, Sebastian turned around in his seat “and said to me, ‘About time, woman!’ ” she said.

“He was so easy-going, you could have given him a coloring book and he would have been just ecstatic,” she said of the family’s recent Christmas, showing off Sebastian’s coloring-mostly-in-the-lines on a Spider-Man comic book.

That said, he loved the electronic LeapFrog game he got, she added.

“I think because all of his brothers and sisters had hand-held games, I think he thought he was part of the pack,” she added. ‘he was a good person’

Saturday afternoon, sisters Marissa, 10, and Morgan, 9, and brother Gabriel, 7, assembled photographs of themselves and Sebastian into a collage to honor their brother. Gabriel tucked a photo of himself and Sebastian under his pillow so “I can see him when I wake up.”

Brother Zachary, 15, was out of town Saturday.

Sebastian played hide-and-seek and Chutes and Ladders with his siblings, usually losing, Marissa said. “He was bright and funny,” she added.

“He was a good person,” sister Morgan said. “When we played Simon Says, he said, ‘Pull your pants down,’ and we did, and all ran upstairs in our underwear,” she explained with a giggle.

Family friend Carol Voigt, a para-educator at Graham Elementary, called Sebastian a gentle, kind soul always ready with a wave and a smile.

“This is a tragedy,” she said. “I think they need some mats, some webbing” at those shows. “It really needs to be prevented.” At the end of the Dome, 20 to 25 feet off the dirt floor, the family believed they were safe, ensconced in a family event. “We were safe from getting hit by a car, but not from flying pieces,” Jessie Hizey said.

The Pierce Medical Examiner’s Office did not immediately release a cause of death. An autopsy was to be performed today. As members of the media asked city officials and Monster Jam producers about safety Saturday, the show went on. Mammoth trucks with tires 5 feet high howled onto the track at the city-owned Dome for the second of five scheduled weekend shows at 2 p.m. Saturday, hours after the boy’s death.

Producers dimmed the lights and observed a moment of silence before the show, said Earl Anderson, 39, of Everett, who came with his wife, Patty, and two children, Robert, 5, and Erin, 3.

Many fans walked away dejectedly when told the 12,000 matinee seats were gone. Those with tickets rushed toward the doors. Many said they’d take care, but believed Sebastian Hizey’s death was a one-of-a-kind incident.

“I think it’s just kind of a freak accident,” said Ron Jutte of Bonney Lake, who came with wife, Kari, and children Chase, 7, and Cali, 5. “I feel pretty safe,” he added. If the shows were canceled, “How do you explain a situation like that to the little ones?” he asked.

Tacoma Dome and city officials worked with Feld Motor Sports Friday night and Saturday morning to review safety procedures, Arellano said.

“They’ll repeat a safety check before each show,” he added. “Based on our conversations, they’re taking extra precautions.” Before the show, a worker in a Monster Jam T-shirt strung yellow plastic tape across four to six rows of lower seating at one end of the Dome. That wasn’t new, city officials said – it’s one of the usual precautions. No plexiglass barrier surrounds the stands as it does in hockey games.

Monster truck shows are a mainstay of Dome business and a regional draw for families. The trucks – weighing 9,000 pounds or more – drive over obstacles, pop wheelies and engage in competitions. They’ve been revving up fans in the Dome for more than 20 years, and Feld has “a stellar safety record,” said Mike Combs, the city’s director of public assembly facilities. No similar incident has ever occurred, he added.

The city issued a statement of condolences to the victim’s families.

“The Tacoma Dome takes the safety of its customers very seriously,” and the city is working with the promoter on the investigation, the statement added.

The investigation will be conducted by Feld Motor Sports, with participation from the Tacoma Police and Fire departments and Dome staff, Arellano said. Police began their investigation Friday night.

Feld also issued a statement of sadness and promised the company “is looking into this tragic accident as the safety of all our customers is our top priority …”

“All of us at Feld Motor Sports and all the Monster Jam drivers and crew extend our deepest sympathies to the families involved,” the statement said.

The Seattle Post-Intelligencer reported that Bill Easterly, senior director of operations for event promoter Monster Jam, described the driver of the truck Natural High as “absolutely devastated.”

Arellano left a voice mail message of condolence for the family, said Dwyer, Sebastian’s mom. No one from Feld called the family, the parents said.

Photographs and descriptions of other monster trucks on the circuit appeared on monsterjamonline.com Saturday evening, but Natural High was not among them. Natural High also did not perform in Saturday night’s show.

Natural High is owned by Kelvin Ramer of Watsonville, Calif. According to the truck’s Web site, it debuted in 2004 and has appeared at numerous truck shows and on television.

Ramer could not be reached for comment late Saturday.

What many in the stands Friday night saw was horrific.

Debra Sharp’s son Shane, her 4-year-old grandson and her son’s girlfriend sat in the same Section 11 B at the east end of the Dome as the victims. Metal debris fell at their feet.

Sharp, who’d been sitting nearby, ran toward the chaos.

“I saw them one minute, then I didn’t see them,” she said. “Everybody was screaming, looking for help.”

The adult victim held his throat, tried to walk and collapsed, she added.

“The blood was everywhere,” she said. “My son’s girlfriend just covered my grandson’s face.”

Sharp and Jessie Hizey said the show continued despite the grave injuries. It took more than 10 minutes for medics to arrive, Jessie Hizey said.

“People were actually throwing drinks on the ground to get the security’s attention, trying to yell,” Sharp said. “The show just kept going on.”

Sebastian and the adult who were injured “got very quick attention” from paramedics, the city’s Arellano said.

The show continued because officials feared calling a halt to it could cause an exodus and that would hamper paramedics working to get the victims to the hospital.

There was only 15 or 20 minutes left in the show, and an orderly exit was best, officials believed.

Jessie Hizey is incensed the show wasn’t stopped.

“The least they could have done was stopped the show,” he said. Once the paramedics reached Sebastian and the injured man, everything in that area was already cleared out and they were near the doors, he added.

“I’m just personally disgusted with the way they handled it. They had no consideration” for the family, Jessie Hizey said.

Tickets to the show cost $23 per adult and could be bought for half price with a coupon for kids

Mike and Shawna of Bremerton were concerned when they heard about the accident, but it didn’t prevent them from bringing son, Christian, 3, to his first monster trucks show.

“As long as it’s checked an everything’s safe,” it should be OK, Mike Wernke said. “He’s pretty stoked,” he added, pointing to his son.

As for the accident, “Terrible things happen everyday in life,” he said.

Kris Sherman: 253-597-8659

Staff writer David Wickert contributed to this report.