A guy who wasn’t even their is a source of information? Ohhhkayyy.
Maybe the best outcome at this point is if they find him dead by a self-inflicted gunshot, before he kills anyone else.
Well - read it again? He’s the bar owner. The perp lived next door. The implication is that everyone involved were “regulars”. He knows or knew everyone involved.
It makes perfect sense to me. YMMV