Well, without more specific details about this 'The Unlikely Murderer Based on True Story', it's hard to say exactly who the murderer was. It could be someone who seemed completely harmless or had no obvious motives at first glance.
Yes, it is. There are many real - life events that can inspire such a story. Maybe it's about a criminal who hides his identity while living upstairs, and the discovery of his true nature could be based on real criminal cases where neighbors were unaware of the danger living so close.
Yes, 'American Murderer' is based on a true story. It aims to present a fictionalized account of actual incidents, staying true to the essence of what happened while adding elements for dramatic effect.