I wish to thank Charles Sheridan for his expertise in the study of stress and for his lengthy mentoring of me through the initial stages of this work. James Collins and Jay Hewitt provided extensive help, especially in the area of statistics. Nicole English, with her expertise in computer software, provided indispensable assistance in converting the format of the National Vietnam Veterans Readjustment Study data from the SAS of the 1980s to the SPSS of the 1990s. Cathy Burnett was especially helpful in the study of capital punishment, and Patrick Peebles in the historical study of the Nazis. Peter Singelmann, Neil Bull, and James Galliher also helped with the sociological perspective. David Grossman, as an army officer, has written and presented on the idea of PTSD symptoms resulting from killing and has given valuable advice. He and Joanie Connors, Jean Maria Arrigo, David Lisak, William Chamberlin, and Gladys Frankl all helped bring about the symposium on this topic at the American Psychological Association in 2000, which generated a great deal of lively and helpful discussion.
I also want to thank the innumerable unnamed individuals, including scholars, veterans, and interested friends, who have listened to me discuss the subject and provided a wide variety of new ideas, leads, and perspectives. There were many who thought they were having only a casual conversation, or a chance to learn a little more themselves, but the collection of ideas over the years has made this book possible in a way that could never have happened otherwise.