IMO I do not think RA had previously targeted the girls or knew them in any way. I am open to being wrong about this, but here is what I envision.
I do think he went to the trails with possibly the idea of committing a crime in his mind. I mainly say this because of how he parked at the CPS building, backing in as if to conceal his plate. I also was going to add the fact he carried weapons to walk a trail as evidence of this too, but I know some people always carry their gun with them, so I am unsure on that one. I think I'd have to know what was typical for RA. Did he usually leave it at home or bring it with him?
I think he didn't attack or kill the three juveniles he first passed because he felt more exposed in that area and/or three people are a lot more difficult than even two. I believe him concealing his face and walking with his head down, as witnessed by those witnesses, was because he did intend to do something criminal and didn't want witnesses to be able to describe him well. Perhaps something set him off this day and made him angry, so he drives to the trails, where maybe he has gone before to honestly clear his head, but he has had thoughts of doing something like this before and decides today is the day if he can find a suitable victim.
I believe he passed A and L previously before coming up behind them in the video. This could be why A decided to start filming. It would seem odd to pass someone who was headed back towards the trailhead and then all of a sudden, they do an about-face and are coming back at you. And perhaps he looked at them oddly the first time they crossed paths or did something to get their hackles raised. I believe he chose them because no one else was around - I think he looked at this before deciding to turn around and go attack them - and he could quickly get them "down the hill" and away from anyone who might come along soon. This is all just my speculation but I can see it happening this way and not being pre-targeted to these girls.
I do think he went to the trails with possibly the idea of committing a crime in his mind. I mainly say this because of how he parked at the CPS building, backing in as if to conceal his plate. I also was going to add the fact he carried weapons to walk a trail as evidence of this too, but I know some people always carry their gun with them, so I am unsure on that one. I think I'd have to know what was typical for RA. Did he usually leave it at home or bring it with him?
I think he didn't attack or kill the three juveniles he first passed because he felt more exposed in that area and/or three people are a lot more difficult than even two. I believe him concealing his face and walking with his head down, as witnessed by those witnesses, was because he did intend to do something criminal and didn't want witnesses to be able to describe him well. Perhaps something set him off this day and made him angry, so he drives to the trails, where maybe he has gone before to honestly clear his head, but he has had thoughts of doing something like this before and decides today is the day if he can find a suitable victim.
I believe he passed A and L previously before coming up behind them in the video. This could be why A decided to start filming. It would seem odd to pass someone who was headed back towards the trailhead and then all of a sudden, they do an about-face and are coming back at you. And perhaps he looked at them oddly the first time they crossed paths or did something to get their hackles raised. I believe he chose them because no one else was around - I think he looked at this before deciding to turn around and go attack them - and he could quickly get them "down the hill" and away from anyone who might come along soon. This is all just my speculation but I can see it happening this way and not being pre-targeted to these girls.