Judith Jarvis Thomson; Killing, Letting Die, and The Trolley Problem, The Monist, Volume 59, Issue 2, 1 April 1976, Pages 204–217, https://doi.org/10.5840/monis.

The Trolley Problem Mysteries considers whether who turns the trolley and/or how it is turned affect the moral permissibility of acting and suggests general proposals for when we may and may not harm some people to help others.