Perpetrator trauma, also known as perpetration- or participation-induced traumatic stress (both abbreviated PITS), occurs when the symptoms of posttraumatic stress disorder (PTSD) are caused by an act or acts of killing or similar horrific violence.
Perpetrator trauma is similar but distinct from moral injury, which focuses on the psychological, cultural, and spiritual aspects of a perceived moral transgression which produces profound shame.
As a psychiatric disorder
The DSM-5 addresses the idea of active participation as a cause of trauma under the discussion accompanying its definition of PTSD, and adds to the list of causal factors: “for military personnel, being a perpetrator, witnessing atrocities, or killing the enemy.”
There has been some study with combat veterans, people who carry out executions or torture, police who shoot in the line of duty, people who commit criminal homicide, abortion staff, and others. Much of the study was previous to the official definition of PTSD, and symptoms have shown up in personal stories throughout history, and in the keen observations of the writers of great literature, most notably Macbeth by William Shakespeare.
Indications from all studies that have considered the question of severity have indicated that symptoms tend to be more severe for those who have killed than for other causes of traumatization. One study  using the U.S. government data base of American veterans of Vietnam  has suggested that the pattern of symptoms at least in combat veterans may be different in those who said they had killed as opposed to those who said they had not, with intrusive imagery (dreams, flashbacks, unwanted thoughts) being more prominent along with the explosive outbursts of anger, and concentration and memory problems being less prominent. To a lesser extent, hypervigilance, a sense of alienation, and the non-PTSD symptom of a sense of disintegration were also found greater as a matter of pattern for those who answered yes on killing. Additionally, alcohol and cocaine abuse appeared to be more severe.
Compared to the victim form of being traumatized, there are different dream motifs reported. While the eidetic dreams – that is, those that are like a video of the event playing in the head – can be experienced as they are with traumatized victims, other motifs also appear more commonly One is that of having the tables turned and being the one killed, or being very vulnerable in the same situation. Another motif is that of the victims accusing the dreaming person or demanding to know why he or she did it. Also possible is a motif of the self being split in two so that the killer part of the person is seen as actually being a different person.
Therapies that have shown some effectiveness in the treatment of perpetrator trauma include group therapy, eye-movement desensitization and reprocessing, Time Perspective Therapy  and understanding how common the problem is. Those who suffer, many of whom participated in violence as a matter of social expectation, find it beneficial to know that they are having a normal reaction to an abnormal situation, and are not uniquely cowardly or crazy. Traditional remedies of atonement, forgiveness, and bearing witness have also stood the test of time as being helpful. More vigorous studies are needed for all these suggestions, as well as common PTSD therapies that have not yet been thoroughly explored with the distinction of perpetration versus victimization in mind.
Other proposed treatments have been proven to be ineffective. The “flooding” technique, technically called Prolonged Exposure, which desensitizes the sufferer of trauma by repeated exposure to reminders of it in controlled settings, appears to be a bad idea, counter-indicated when the trauma involved being active in inflicting harm. It may be that expressive writing, which most people find helpful in working through their traumas, instead increases anger in soldiers. Differences in what physiological mechanisms in what pharmaceutical drugs might be useful in therapy are not yet known.
Cycles of violence
Several of the symptoms are capable of causing or allowing for renewed acts of violence. The outbursts of anger can have an impact in domestic violence and street crime. The sense of emotional numbing, detachment and estrangement from other people can also contribute to these, along with contributing to participation in further battle activities or to apathetic reactions when violence is done by others. Associated substance abuse may also have connections to acts of violence.
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