[John Jamieson]

"You left us a phone number"

I think it's likely that the snipper didn't think he was leaving a phone number, just the "message" "911". Police are using it to bait him into calling them. Pretty sharp if that's what's going on. They have already begged him to write to their POB.

[doglot]

That is the only answer that made sense to me, but he (they) are too smart for that.