Now, tbh, i really like watching and listening to Ives speaking about the case. He has an analytical, if not to say, engineer's, mind, and his speech is very succinct. No excessive emotions, no extra information, just facts.
However, one thing that he says makes me wonder exactly the opposite. He said, there was no doubt that BG was responsible for the murders.
Thinking logically...
All we see is the man on the bridge with an odd gait. Unless the video extends (and we don't know what it shows), I am not a 100% sure that it is the same guy who approached the girls and marched them down the hill.
There were people around, maybe it is a passer-by. (It is another thing that the guy never came forward, but maybe he was an illegal alien from somewhere around?)
Maybe it is a red herring?
Maybe he wore a mask, and maybe one of the descriptions fits this guy (it is interesting how the sketches of the OBG and the NBG differ in the amount of details - really, I'd trust NBG sketch more because this is the same I would remember from a chance meeting with someone I didn't know).
At this point in time, I believe, the ISP has reached two dead ends, with two big cases. Maybe it is the result of being overwhelmed, because they have to do their daily job, too.
Really, it calls for two target groups, who will start from the very beginning. Before the murders.