Specifically to the article: the section titled “A murderous nurse at work—or just coincidence?” Correlates the shifts during which a particular nurse works and

Specifically to the article: the section titled “A murderous nurse at work—or just coincidence?” Correlates the shifts during which a particular nurse works and suspicious deaths occurring. If anyone has any know-how to interpret the following diagram, I’m open to some help here. Sorry if it annoys you to hear a devil’s advocate defending a potential murderer, but what if said nurse was just incompetent and people took advantage of her? (Or she was the primary person willing/forced to work shifts known to be ripe with gang activity.)