You really can't base anything off of a video and a couple pics. The police said he was shaking and nervous in the interview. Doesn't sound like he had it all together to me.
The only way I can see me leaving all of those things behind is if I was just stepping outside to meet someone for a quick chat in the backyard or on the porch or something. Or maybe he just went out to his car to talk, and was convinced to go for a ride for a bit longer of a talk. When I was that age, I might have done that. But leaving without my keys or anything would only have happened if I thought my friend was going to run to the store down the street and then right back.
