After all, she finished in 1 hour and 21 minutes, meaning she ran a blazing 6:15 mile. The women’s world record is held by Florence Kiplagat, for a time of 1:05:09.

What was even more incredible — and what tipped race timer Josh Stern off to the fact that something fishy was afoot — was that Seo ran faster miles in the second half of the race. Though runners often try to maintain a steady pace for the whole shebang, exhaustion forces most to slow down as they near the finish line.

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As noted in the Miami New Times, Stern voiced his concerns to race director Matt Lorraine, but Seo convinced him that all was on the up-and-up. Her second place finish stood.

Someone, though, wasn’t convinced and tipped off Derek Murphy, an independent marathon investigator. Murphy, a former distance runner himself, has dedicated his time away from work trying to bust cheating road warriors by using the 21st century’s best tools: data collected in our interconnected world. He posts his findings to his blog, Marathon Investigation, which he maintains from his home in Ohio.

The work has real world consequences, too — he has caught several runners who qualified for the Boston Marathon by cheating, taking spots from honest runners.

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“I think most people aren’t aware of how much cheating goes on in marathons,” Murphy told NBC last month.

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Murphy began investigating and quickly learned that Seo had, indeed, cheated by skipping about a mile and a half of the race. As a result, she has been retroactively disqualified from the half-marathon and was expelled from the Dashing Whippets, the team with which she raced.

“As some of you may be aware, one of our members intentionally cut the course at a Half Marathon this past weekend. The member in question has admitted to cheating, has been officially disqualified from the race, and has apologized to the DWRT Board,” the organization said in a statement.

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In a lengthy blog post, the sleuth explained how he exposed the runner.

Murphy began by examining the official results from the race tracker — a small electronic chip runners wear that incrementally tracks their time during a race — that caught Stern’s attention. Her pace during the first 10 kilometers was 7:09 per mile. During the last 11.08 kilometers, it increased tremendously to 5:25 per mile.

Seeking further data, he turned to her account on Strava, a social media app where runners and cyclists post their times. She had posted but rather than let the app pull her info from GPS data, she manually entered just her time, distance and pace.

Stranger still, later that day, she posted the full entry showing more information: her path, splits, cadence and heart rate. Though it showed that she completed the entire course, something struck Murphy.

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He wrote, “She had this labeled as a run, and the total time *almost* matches her original time for the 1/2 marathon. The cadence data is more consistent with what you would expect on a bike ride, not a run.”

The app includes a (somewhat hidden) feature that indicates what time a run (or bike ride) took place. When Murphy checked this, he found this second posting showed “that she actually covered this course in the afternoon — long after the race was complete.”

Next came the bombshell. He observed in official post-race photos that a Garmin 235 fitness tracking watch was wrapped around Seo’s wrist. So he purchased the high resolution photographs and zoomed in.

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It displayed close to the proper time, 1:22:07.

But the incorrect mileage: 11.65 total miles.

Murphy wrote, “This shows about 1-1/2 miles were cut. Her total time on the watch is 22 seconds longer than her initial finishing time — showing that she did indeed start the watch when she crossed the starting line.”

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He told the Miami New Times that he informed Seo of his findings Monday, but she continued claiming her time was legitimate. Until later that night, when she posted an Instagram post she’s since removed. Murphy grabbed a screenshot, though.

“I made a HORRIBLE choice,” it read. “I wasn’t feeling well so I CUT THE COURSE and headed to the finish line. I got swept away in the moment and pretended I ran the entire course, when in fact I CHEATED and should have DISQUALIFIED myself.”

Murphy told the Miami New Times that Seo finally admitted to riding her bike along the course later in the day to cover her tracks. He concluded:

Whether the decision was pre-planned or spur of the moment, her actions after she crossed the finish line are what cannot be justified. This wasn’t a case of getting tired and calling it a day. This was an intentional act of deception as evidenced by her admission that she biked the course to try to cover her tracks. Had she just gone straight back to her hotel, she would have been initially disqualified and the correct runners would have received the awards.

“Had she just admitted what she did, I never would have heard of her, nor written about her,” Murphy told the Miami New Times. “But going back and biking the course to cover up … that’s unheard of.”