Although the earbud story is odd, I think it possible that it was in his lap at some point, it's his using that to explain his blackout "story" that is not believable, but that's, what he thought of at the time. The only reason I think it's important is that it incriminates him. It would imply the victims head was in close proximity to his lap at one point. What was it doing there? Of course the earbud was torn off in a struggle, but how would it somehow stay stuck on his body somewhere and eventually fall into his lap? Even if he had already put her body in the trunk it seems a strange place to end up after he was upright and walking around. That being said, I believe immediately after chasing her down he killed her right in that general area. Either pulled her into a more isolated area or the attack happened in the car itself. He then placed her body in the trunk, and drove around either looking for a place to hide the body or going to a preplanned location. The only thing that is a mystery is the 8:00 sighting by the neighbor. I guess it's possible that he saw her 15 minutes earlier, or if it was closer to 8:00 pm, Rivera could have been following her and even called out to her. This might explain the fit bit activity, as it may be the first time it indicated fear, and her heart rate started to go up at that time. Then another increase when she was running for her life , then fighting and being overcome by her killer, all in a matter of 40 mins. After he had dragged, then carried her body into the cornfield he went back to his car and probably, once over his adrenaline rush, tried to decide what to do next. This is the moment in his story that he tells investigators is when he " came to." He has already killed her so what better place to insert it. The question is, what did he do after That? Get cleaned up somewhere? Dispose of the weapon, clothes and phone at the farm? There are many gaps to fill in.
