«I think most peo­ple aren’t aware of how much cheat­ing goes on in marathons.» Were you aware? I was­n’t. But Derek Mur­phy, an inde­pen­dent marathon inves­ti­ga­tor, should know. He recent­ly took par­tic­u­lar care to exam­ine the case of Jane Seo, a food and fit­ness writer in New York City. She fin­ished sec­ond among the women in Sunday’s Fort Laud­erdale Half Marathon in 1 hour and 21 min­utes, a blaz­ing 6:15 mile. But she cheated.