I have never killed someone and if I had, I'm pretty certain it would F me up for a long time.

[spin]

88. There is an excellent chance that killing another person in legitimate self defense ...

will cause significant psychological problems.

Often police officers who kill another person even when absolutely necessary undergo counseling.

Law Enforcement Traumatic Stress: Clinical Syndromes and Intervention Strategies

Laurence Miller, Ph.D.

***snip***

Police officers generally carry out their sworn duties and responsibilities with dedication and
valor, but some stresses are too much to take, and every officer has his or her breaking point. For
some, it may come in the form of a particular traumatic experience, such as a gruesome accident
or homicide, a vicious crime against a child, a close personal brush with death, the death or
serious injury of a partner, the shooting of a perpetrator or innocent civilian, or an especially
grisly or large-scale crime; in some cases, the traumatic critical incident can precipitate the
development of a full-scale posttraumatic stress disorder, or PTSD (Miller, 1994, 1998c).
Symptoms may include numbed responsiveness, impaired memory alternating with intrusive,
disturbing images of the incident, irritability, hypervigilance, impaired concentration, sleep
disturbance, anxiety, depression, phobic avoidance, social withdrawal, and substance abuse.

***snip***

In the United States, two-thirds of officers involved in shootings suffer moderate or severe
problems and about 70 percent leave the force within seven years of the incident. Police are
admitted to hospitals at significantly higher rates than the general population and rank third
among occupations in premature death rates (Sewell et al, 1988). Interestingly, however, despite
the popular notion of rampantly disturbed police marriages, there is no evidence for a
disproportionately high divorce rate among officers (Borum & Philpot, 1993).
http://www.aaets.org/article87.htm