The machine most likely to kill an American has been the automobile.Car crashes killed 33,561 people in 2012, the most recent year for which data is available, according to the National Highway Traffic Safety Administration. Firearms killed 32,251 people in the United States in 2011, the most recent year for which the Centers for Disease Control has data.
There is a study published in the journal Social Cognitive and Affective Neuroscience which brings science a step closer to understanding exactly what goes on in the brain of a killer.
https://time.com/3816212/brain-murder-morality/