That's very true that the bridge put a barrier between himself and any witnesses. To me, though, the bridge, along with the formal end of the trail and the creek itself, worked in conjunction to corner the girls, leaving them no way to go back the direction from which they came. In all reality, somebody could have entered the trail and gotten to the north end of bridge before he even reached the south end. Or they could have started crossing while he and the girls were walking down below. Even if he'd watched for other people for awhile on the north side, there was no way for him to know who might enter the picture in the minutes it took for him to cross, or in the time it took for them to go DTH and through the creek. Imo, it just shows how very risky it all was. The element of the unknown in a crime like this makes me question how much thought he really put into it before hand, things such as where to park, where to exit, etc. I don't think there was much planning involved, or else he could have planned something with less risk. IDK...just tossing around the idea. And I guess if anyone had entered the picture unexpectedly, he could have just not gone through with it.