The
something that some people see as an item getting tossed into the back of the car, or the footwell, looks to me like it's going on outside of the car, not inside... more like
@floridagrrl 's analsyis (i.e. legs about to go in, but then retreating, then back in). I also see movement of the right arm of the passenger just as she's landed in her seat - possibly lifting the arm to reach over to her left for the seatbelt. Assuming this is Libby and she got into the car willingly, having been sold a story she trusted, I can see that it's possible she slipped just as she was getting into the car, hence the apparent kerfuffle at the passenger door. There was fresh snow on the ground at the time (you can see how there's no snow under the car as it drives off), so I can imagine how easy it would be to slip as you're trying to climb into a car. If she does in fact put on her seatbelt, this does make me think that at that point she wasn't under any kind of duress and had every reason (and right) to believe she was safe.
I know it goes without saying, but it makes me (and I'm sure all of us) so angry and outraged that someone can con another person into trusting them and do them and their loved ones the worst of all possible harm.