My theory: Mollie leaves home around 7:30 p.m. for her jog with her fitbit, cellphone and wearing her jogging clothes. She heads east on Des Moines Street and makes turn to the south on West Pershing. She continues on to Clay Street where she turns south. At the time she makes it to the car wash at the corner of Clay and 2nd Street the perp has already came into town, passed the truck stop where he is captured on camera and is atop the railroad bridge on Clay Street where he sees Mollie make the turn on to 2nd street, passing the camera at the car wash. He knows the area and can see her jogging down 2nd and knows that 2nd Street ends at a cornfield and also has streets that run parallel. He sees her make the turn on to Mills Street and takes the first parallel street before Mills, which is Williams. He can see her across the park approaching the intersection of Pleasant and Mills. He even has time to wait at the park as she approaches. When she approaches he pulls in front of her and grabs her and heads down Pleasant heading west to Boundary Street. He turns north on Boundary Street and makes the turn to 385 heading east. He knocks her out near the corner of 385 and V21 and that is where the fitbit registers no movement or increased heartbeat. He takes her south on V21 and disposes of her and/or the cellphone around route 85. Perp either leaves area or goes back to Brooklyn a couple hours later and enters town the same way, passing the truck stop and maybe stopping to wash his car of all the dust on the way back in to town or stops at Casey's for a drink. This theory accounts for every red spot on the FBI map. I take the eyewitness testimony with a grain of salt. I posted the possible jogging routes below and of course, my theory has slight variations.
O.K. lets go with that; but it's been suggested that she did homework on a laptop after her run; also there might be other mobile phone data that might contradict your scenario.