Look at that. That's the face of evil. That's the face of a "kid" who just brutally raped and destroyed a six year old baby, and is now driving around with his horrified mother. That's the face...nothing. No emotion.
I'm not a psychologist but, maybe. However I do, unfortunately, have a lot of experience with borderlines (my mother in law, an aunt by marriage and a few opposing parties in my cases), and it doesn't smell like it to me. In my experience, borderlines like to talk, generally. A lot. They think they can explain away anything. They feel they can b.s. you or force you to accept their viewpoint, or show you that their behavior was compelled or excusable.
They tend to be over the top and have quick bursts of anger reactions. Very dramatic. Always having a major issue or problem. This kid was known to be pretty shy and we've heard nothing about any serious, on-going behavioral issues.
Not being an expert in psych issues, I think the intense violence and horror of the crime coupled with his attempts to manipulate, fear only shown for himself (stomach heaving the car), impassioned face at the vigil and in the car (I would expect a borderline to have public displays of emotion and to make it about them - hero or devastated insider), and his ability to turn off his emotions at the police interview and yawn and stretch when they weren't in the room, as a direct and very opposite exhibition of emotion from his earlier, apparent grief or horror stricken catatonia, we are dealing with someone much more sophisticated and scary than a borderline.
But that's my guess.
Yes.