https://www.washingtonpost.com/news/morning-mix/wp/2017/02/23/how-an-ohio-blogger-discovered-a-runner-a-harvard-grad-cheating-in-a-half-marathon-across-the-county/?utm_term=.2ccc7e623632

I'm kind of amazed that there are people out there dedicated to finding marathon cheaters, but its hilarious how he caught her. There was other stuff that initially raised suspicion, but he finally got a hi-res photo of her crossing the finish line, and he zoomed in on her Garmin watch and saw that it read only 11.65 miles instead of the full 13.1. She cut almost 1.5 miles of the race to finish in 2nd place. She went through big lengths to try to cover up, including carefully biking the whole route later that day to match her claimed time so she could post those results online claiming it was her run, but the cadence didn't match running and she couldn't obscure the time as being after the run either.