Shining Promise, Dark Mystery : Murder: Friends of slain honors student Stuart Tay struggle to understand how a life brimming with brilliance slid toward the abyss.

The 17 years of Stuart Tay’s life could not have been more strikingly different from his last day.

The bespectacled honors student with a renaissance range of talent lay crumpled in a muddy back-yard grave in Buena Park on a chilly New Year’s Eve, his reputation soon to be tarnished by whispers of a robbery plan gone sour and a love triangle involving his accused killer.

Police say that five teen-agers from Sunny Hills High School in Fullerton--most of them honors students from affluent families--planned and carried out Tay’s murder, having grown suspicious that he would betray them in a planned heist of computer parts.

They allegedly lured him into the garage at one teen-ager’s home, ostensibly to show him a handgun he wanted to purchase, then beat him with baseball bats and a sledgehammer. When he still showed signs of life after 20 minutes of beating, they poured rubbing alcohol down his throat and sealed his mouth with duct tape.

A private investigator hired by Tay’s family suspects that Robert Chan, 18, the alleged mastermind of the killing, was driven partly by a fury that Tay was dating a girl who spurned Chan some time ago. But police have explored and discounted that theory.

Days after his death, those who knew Tay well struggle to grasp what happened, searching their memories to find the point when a life so brimming with promise was drawn into a deadly abyss.

Others, while surprised that Tay would come to such a gruesome end, are less than shocked by allegations that he was involved in illegal activity.

These were students who had exchanged glances when Tay squealed into the school parking lot in his parents’ silver Mercedes convertible. Again and again, they had heard the rumors that Tay carried $100 bills, that he boasted of being involved in illicit computer hacking and counterfeiting. One family friend said Tay had a fascination with such shady pursuits.

His closest friends at Foothill High School in Santa Ana dismiss talk like that, saying anyone who believed it did not know Stuart. Maybe he was a little too cocky, a shade too arrogant, they say, and maybe he liked to talk big. But beneath the swagger was a sensitive and good-natured young man who was deeply loyal to his friends and unfailingly courteous to elders.

Here was a teen-ager, after all, who avoided rowdy high school beer parties and did not smoke, preferring to spend weekends with the Safe Rides club, whose members took turns providing rides home for drunk classmates. Here was a student who occasionally wore suits and ties to school when peers sported baggy jeans and T-shirts; the one who prepared flash cards for his friends to use in studying for the college entrance exams.

This was the son who unfailingly came home for dinner on time, took out the trash and did the yardwork at his family’s sprawling, gated home in Orange. Tay was the student who brought chocolate-covered raisins, wrapped with a bow, to his guidance counselor for Christmas, because he knew she loved them. He escorted his former English teacher to a lavish hotel brunch, making sure he drove his mother’s car because it was cleaner than his own.

That teacher, Joan Kasper, recalls wistfully how Tay recently treated her to a buffet brunch at the Ritz-Carlton hotel in Dana Point. She said he was very upbeat that day, and was “gallant” and “charming.”

“We talked of so many things, especially of his future. He was very much focused on that, and it was a very bright future,” Kasper said of Tay, who had applied for admission next fall to Princeton University, UC Berkeley and UCLA.

“He talked about how it felt to be in love for the first time (with fellow Foothill student Jennifer Lin) and showed me a pocket watch she had given him for his birthday.”

Kasper, who was Tay’s honors English teacher last year, remembers him as a student who often took the lead in provoking and prodding classroom discussions. Friends recall that he often sparked heated debates in civics class, testing how far he could take arguments on such controversial topics as the role of women in the military.

“He loved to play the devil’s advocate,” said friend and classmate Nathaniel Stracker, 17.

Tay’s acquaintances said he was not only interesting and bright but a good friend.

“When I needed help doing stuff, he was always there,” said Don Chennavasin, 18, one of Tay’s closest friends.

Chennavasin and another friend, Jack Oak, 17, recalled a skiing trip they took with Tay to the Mountain High resort over Christmas vacation. Oak said they dubbed Tay “psycho-man” because he was braving jumps and zooming around the slopes.

Tay was a distinguished student, carrying four honors classes and one advanced placement class this year. In his sophomore and junior years, he had already qualified for college credit in biology and U.S. history by passing advanced placement tests, said his guidance counselor, Genevieve Koerner. He was planning to take the tougher of two placement tests in calculus this spring. He aspired to be an ophthalmologist or a plastic surgeon.

But to Koerner, Tay also stood out for his wide range of talents and interests. He was an amateur photographer, wrote poetry and played the piano in a rock band. He climbed Mt. Whitney with his Boy Scout troop. He founded an Asian culture club on campus, and belonged to the politically conscious Junior Statesmen of America.

He ran his own business buying, selling and repairing computer components. And he loved to tinker on computers himself, using as his password Depeche Mode, the name of his favorite rock group.

Koerner said Tay, with one younger sister, came from a close-knit family that put a premium on sharing conversation over dinner every night. His parents, a homemaker and an obstetrician, emigrated from Singapore years ago and worked hard to establish a secure lifestyle, moving from Fullerton to a large, custom-built home in Orange when Tay was midway through sixth grade.

So dedicated was his mother to her son’s school life that she drove every day from Orange back to Fullerton so Stuart could complete the sixth grade at his old school, one teacher recalled. News of Tay’s death and its seamy circumstances stunned his sixth-grade teacher at that school.

“It blows my mind,” said Ann Lehman, who taught Tay in his final year at Sunset Lane Elementary School in Fullerton. “He was a loved, self-confident child.”