SQUAMISH, British Columbia >> The race was tough and the conditions dreadful — 2.4 miles of swimming, 112 miles of cycling and 26.2 miles of running, mostly in freezing rain — but Susanne Davis crossed the Ironman Canada finish line last July certain that she had won her category, women age 40-44.

Davis, who comes from Carlsbad, California, and is one of the top triathletes in her age group in the world, had been first out of the water and first off her bike — she was sure of it. Spectators using a mobile phone race app that shows competitors’ relative positions called out encouragement, telling her she was ahead by a comfortable 10 minutes. As she ran, Davis looked out for rivals, asking the age of every woman she passed or who passed her, and encountered none from her age group.

Yet there she was, accepting the medal for second place at the awards ceremony the next day, five minutes behind a Canadian triathlete named Julie Miller who seemed to have materialized from nowhere and somehow won the race.

Miller, a mother of two young daughters, is a mental-health counselor specializing in body-image disorders here in Squamish. She is also a serious triathlete with a long record of success. Before last year’s race, in Whistler, she had also won her division in the 2013 Ironman Canada, the 2014 Vancouver Triathlon and the 2014 Long Course World Championships in Weihai, China, where she competed for Canada and where her win briefly made her the world champion for her age group.

Davis knew none of that. All she knew was that in more than three hours of hyperconscious running, she had not seen Miller once.

The winners were announced: Julie Miller first, Susanne Davis second. “She didn’t come down and shake our hands,” Davis said, referring to Miller. “In my entire 20 years of racing, I’ve never had that happen. That’s when I looked at her and said: ‘Gosh, I didn’t see you. Where did you pass me?’”

Miller replied that she had been easily recognizable in her bright green socks and then all but ran off the awards stage, Davis said, telling Davis that she would see her at the world championships in Kona, Hawaii.

Davis compared notes with the third- and fourth-place finishers. They, too, were mystified. They had not seen Miller on the course, either.

This odd series of events eventually touched off an extraordinary feat of detective work by a group of athletes who were convinced that Miller had committed what they consider the triathlon’s worst possible transgression. They believed she had deliberately cut the course and then lied about it.

Dissatisfied with the response of race officials, they gathered evidence from the minutiae of her record — official race photographs, timing data, photographs from spectators along the routes, the accounts of other competitors and volunteers who saw, or did not see, Miller at various points. Much of it suggested that Miller simply could not have completed some segments of the race in the times she claimed, and all of it raised grave questions about the integrity of her results at Whistler and other races.

Three weeks after winning Ironman Canada, Miller was disqualified from the race, her time erased, her first-place finish voided. Soon after, she was disqualified from two previous races that she had also won. Ironman has barred her indefinitely from its competitions.

“We can’t prove what happened on the course in Ironman Canada in 2015, or what her intent was,” the regional director for Ironman, Keats McGonigal, said in an interview. “People can make their own judgments and decisions. But what we can prove is that it would have been impossible for her to be at specific points at specific times and still get to the finish line when she did.”

Miller denies it all.

“I did not cheat in the Whistler Ironman competition,” she said in an email, “nor would I ever cheat or have I ever cheated in any competition.”

Such stories of cheating inevitably leave many questions unanswered. What motivates athletes to cheat systemically? And how, exactly, did they pull it off?

“It doesn’t really make any sense,” said Claire Young, of Kelowna, British Columbia, who, after Miller was ultimately disqualified, took second place in Ironman Canada. “Most of us are essentially racing against ourselves. There’s no money and no glory. It’s just a hobby, and if you cheat, who are you cheating? You’re only cheating yourself.”

Questions swirled around Miller’s performance as soon as she crossed the finish line at Ironman Canada, on July 26, 2015. The race was held in Whistler, a site of the 2010 Winter Olympics just north of Squamish. Miller finished in 10 hours 49 minutes 3 seconds, a time recorded manually by an official positioned at the finish line and confirmed by photographs and video images of her crossing it.

There was a problem, though: She was missing her timing chip.

Ironman athletes are required to wear timing chips, affixed to Velcro straps they usually wrap around their ankles. The chips are recognized electronically at timing mats positioned along the course, recording an athlete’s time at those points (the interim times are known as splits). Although the Velcro straps sometimes come off, it is practically unheard of for the chip to become dislodged from the strap.

But Miller’s somehow did.

Miller said that the chip had come off as she changed her clothes during the bike-to-run transition. Race records show that, indeed, her chip had recorded a time of 7:17:50 at the end of the bike ride, before going silent.

According to Ironman rules, no chip means no time. Miller was on the verge of being disqualified.

After the triathlon, Claire Young went to a coffee shop in Whistler with her husband, James, also an Ironman athlete. She had finished the race in 11:06:24, right behind Susanne Davis. As far as she had been told, Miller had beaten them both. The Youngs were discussing how odd this seemed when they were interrupted by a woman at a nearby table.

“She said, ‘Are you talking about Julie Miller?’ ” James Young said in an interview. “‘I’m from the same town as her, and there’s no way she won that race.’”

Later that night, the official results, posted online, showed that Miller had been disqualified. Word got out that she had had some kind of issue with her timing chip.

“It didn’t even cross our minds that there might be foul play,” James Young said.

But athletes can plead for reinstatement under special circumstances. That’s what Miller did the next morning. In a confrontation with McGonigal, the Ironman regional director, she argued that losing her chip had been an unfortunate accident that should not disqualify her from the race. He believed her, he said, because parts of her story checked out.

The awards ceremony took place at Whistler’s Olympic Plaza, and three women — Susanne Davis, Claire Young and Marla Zucht — arrived believing that they had taken the first three spots in their division. No one had told them that Miller had successfully argued her way back into first place.

Indeed, few people who had been paying close attention seemed to think that Miller had legitimately won the race the day before. As they replayed the race in their minds, they found things that did not add up. Some spectators and volunteers said they had seen Miller running slowly, outpaced by speedier runners, near the start of the marathon, and wondered how she could have made up for all that lost time.

The marathon course comprises two distinct parts, a loop and then an out-and-back section in which athletes retrace their steps. Each athlete runs the whole thing twice. Some spectators who said they were specifically looking for Squamish athletes to cheer on said that in places where they would have expected to see Miller several times, they had seen her just once.

A few days later, people connected to the race began receiving emails from an anonymous sender identified as “Honest Athlete.” The messages cast doubt on Miller’s performance and cited evidence that seemed to suggest something was awry. Other athletes, including James Young, began to investigate further.

Among other things, Young studied the images taken by cameras positioned along the course and posted on race websites.

Because Miller had no timing chip, there was no official record of her marathon split times. But some photographs showed her running near other athletes who did have timing chips, providing contemporaneous evidence for what time she had reached various points in the race.

In interviews, competitors and volunteers said that as they looked back on other races, they recalled things that had made them suspicious of Miller’s performances. But they had never said anything, they explained, because they had not wanted to make such a grave accusation against a fellow athlete.

An aid-station volunteer from Squamish who was cheering on local athletes in the 2013 Ironman Canada race, for instance, said that based on her position and the number of times she saw Miller, it looked as if Miller had failed to complete all the laps. She thought she might be mistaken. But it happened again in 2015 — she saw Miller just once, when she would have expected to see her twice.

“I thought, ‘Twice in a row?’” the volunteer said. She submitted a report to Ironman officials.

Ironman officials say they were not aware of the other athletes’ concerns until early August, when McGonigal, the Ironman official, received a flurry of angry emails urging him to reconsider the results.

Disqualifying an athlete is not done lightly, Ironman officials said, and they gave Miller ample opportunity to defend herself.

But Miller never produced anything beyond asserting that she had not cheated, not even GPS data from a watch she had been wearing. She was disqualified for good. She was also disqualified from two previous races: Ironman Canada 2013, which officials said she did not complete (and where she said she also lost her chip) and the 2014 Vancouver Triathlon.

Ironman barred Miller indefinitely from its races, citing repeated rule violations — the harshest penalty given to a competitor in memory.

In several email exchanges, on the telephone, and in a brief conversation at the front door of her house in Squamish, Miller declined to be interviewed for this article — saying that she would derive no benefit from trying to explain how she completed the races in the times she claimed. Her critics would find a way to rebut her story no matter what, she said. At one point she promised to provide evidence that she had completed one of the suspect races, but never followed through with the complete information.

© 2016 The New York Times Company