I can't recall which article it was in now, but there are quotes from Detective Loomis about the CL's alibi checking out, and JeM being where he said he was.
That indicates to me that he told LE about both the store visits and which ones he visited, so they were able to go there and confirm that.
Just guessing, but I suspect LE has a good few maps of their own that would really interest us.
Something I forgot about completely but the Brittney Woods case reminded me; do you think all people connected to this case allowed LE access to their cell phone records? Or could LE just pull them without permission? Phone pings would almost certainly help with sorting out who was where, and when. It also might help to see who was calling who, and when. I suppose it's too much to hope for.
One other thing; as JeM seems to have been a bit of a slow worker, and the repairs had been left to the last minute, does anyone think it's possible he may have brought someone along to help? And maybe dropped them off during his morning store trip? That's where a cell phone ping or two might really come in useful. If he did have someone helping him initially, I wouldn't wonder at them keeping quiet, or JeM protecting them, with all the attention that has been generated since.
I am really not sure if anyone could be insane enough to do that though, because how suspicious would that look if LE found out? Unless they are relying on JeM to back them up and explain their innocence, should disclosure become unavoidable.
IMO it's unlikely, I think, but not entirely impossible.