Edited sentence: Also his wife could be said to be an accessory if she testified in court each time that he wasn't a habitual drinker and the drunk driving was unusual.Also the nurse did not seem to be a mercy killer.Dexter killing her could also be seen as his way of defending Harry since she was already dosing him.ETA: The alcoholic repeatedly changes his names and locations after getting off scott free for drunk driving and causing death and/or injury to innocent people.He does so by claiming that he doesn't drink and it was an unusual act and it will never happen again.Malevolent not merciful.Plus it was shown that she kept trophies by means of saving obits of the people she killed.She seemed most likely to be interested in having the power of life and death over helpless people.So he is a serial killer , just one with an unusual methodology.The nurse was definitely more Angel of Death than mercy killer.Therefore he isn't charged with a felony and can legally change his name.With a character like that however , she is probably harmless unless she hooks up with another person like her husband