Hello! This is my first post, so excuse me if I do something wrong x.x
I have been reading through the posts and just wanted to put my input in on the purse/phone topic. Firstly, I feel as though a couple of different scenarios are possible. On one hand, Sierra could have known the person in the car, or at least got in willingly, and was told to leave her belongings. Kind of like a 'you won't need those' sort of thing. So she stashed her belongings and got in the car, presumably with her phone in hand. Maybe the perp got angry at that point because she didn't leave everything and threw the phone out of the car window. The throw could have been in another joking manner, or aggressive to the point that Sierra realized something was wrong, but the perp drove off without giving her the opportunity to get out.
The other theory I have is that she took everything with her and the perp returned at a later time to get rid of it. Maybe he/she thought that if they left Sierra's belongings at her house that it would throw them off the trail somehow. Then again, I see flaw in this unless the perp returned shortly after, while it was dark and minimal chance of getting caught. At the same time, another flaw appears because why would the perp risk the chance of getting caught at all.
Last thing I want to note is that IMO, there was more than one perp or Sierra went willingly. The perps could have caught her off guard enough to kidnap her. Maybe they drove a truck? One perp could have hidden in the back, and while the driver distracted Sierra by asking simple questions, the other perp attakced her and got her in the car.
Again, I might have missed over some information that would contrast with my theories, but this is all in my own opinion how things may or may not have happened.