I think there are even other reasons why someone may not be coming forward even though they are innocent. Like, what if it was someone traveling or just passing through? Or someone who lives in a city outside of this one? I know because we are tuned into websleuths we think everyone watches the news, but I think it is VERY possible to be ignorant of even high profile cases happening in the next town over or whatever. I lived near where a law student was missing and then found murdered in a horrific way and only her torso was found and some of my friends living in that city acted like I was crazy when I brought it up because they hadn't heard anything about it. Not everyone talks about that stuff or watches any type of news system.
Or, maybe he was cheating on his wife/buying drugs/something else horribly embarrassing that he doesn't want to admit and feels like his wife/friends/family/whoever else would find out if he came forward and since he didn't do anything and didn't see anything he justifies not coming forward.
Of course, none of these could be true, but I do think there are explanations for the van guy not coming forward beyond him having to be 100% guilty of this crime.
I am really hoping the van is involved though and that the sketch is accurate. What a waste of misguided resources if not. I mean, of course, their course of actions make perfect sense-they had a witness or two and multiple sightings of the same vehicle. It would just be heart-breaking if that was just some misunderstanding though and the real perp is probably celebrating somewhere that everyone is focused on a van and a sketch of not him.