The turning point comes when Dexter witnesses Mary with a new patient: a man suffering from late-stage cancer, begging for just one more day to see his daughter. Mary preps the lethal injection anyway, ignoring his pleas.
: She was Harry Morgan’s nurse during his hospitalisation for heart disease. Harry realised she was poisoning him and gave Dexter permission to kill her to save his own life and protect future patients. The Kill Ritual dexter kills nurse mary
Dexter stabbed her multiple times in the chest/stomach. In Original Sin , he is shown smiling as he feels her heartbeat fade. The turning point comes when Dexter witnesses Mary