Those of us who are old enough remember O. J. Simpson’s bizarre pursuit of the “real killer” of his murdered wife. And the Saturday Night Live skit where his analysis of football plays spelled out “I did it” on the screen. Now Olympic runner Oscar Pistorius seems to be acting from a similar script.
At this point, we do not really know what happened in the Pistorius case, of course, and he is presumed innocent until found guilty in a court of law.
The phenomenon of killers who claim innocence is very familiar to law enforcement personnel and lawyers, however. There are many different reasons for such claims:
They are lying in order to bolster their case for acquittal.
They are innocent victims of miscarriages of justice of which an astonishing number end up on death row as the Innocence Project confirmed sometimes by using DNA evidence.
Most interesting of all is the case of perpetrators who are actually guilty but do not remember committing the crime.
Can a husband kill and not be aware of it?
Homicides are sometimes committed in a dissociative state where the perpetrator is not fully aware of what they are doing. One of the most intriguing examples involves men who murder their wives while they are asleep (1). As one might imagine, this is a tricky legal defense. Yet sleep walkers do some uncanny things. Men with a history of acting out dreams occasionally attack and kill their wives and some are acquitted due to diminished responsibility.
Whether such explanations are credible or not, they are extremely rare if only because few adults walk in their sleep. A far more common phenomenon is for killers who are covered in blood and holding the murder weapon to claim complete innocence.
Psychologists have a very good explanation for most such cases – amnesia. Calling it “amnesia” is somewhat confusing because that term usually refers to an inability to recall a memory that is actually stored in the brain.
The argument is that highly stressful events temporarily interfere with the laying down of new memories (or cause anterograde amnesia). This is not too surprising in view of what we now know about the generalized impact of stress hormones on brain function. Thus when elderly people go through a stressful experience, the symptoms of senile dementia worsen.
One plausible reason is that during the fight-or-flight response to stress, more energy resources are diverted into skeletal muscles and away from other functions including digestion and the brain.
Whatever the precise mechanism, a stressful experience, such as killing one’s wife can interfere with forming a memory for that event. So the big reason that many perpetrators claim innocence is that they have no memory of doing what they were accused of doing. Some experts believe that partial, or total impairment of memory formation for the crime is characteristic of the majority of homicides (with reported rates varying from 10-70 percent, 2). One might imagine that if the murderous act is out of character that it would be more highly stressful than is true of a habitual killer.
If so, then when nice guys murder their wives, they would be expected to have little memory for their violent act.
2. Porter, S., Birt, A. R., Yuille, J. C., & Herve, H. F. (2004). Memory for murder: A psychological perspective on dissociative amnesia in legal contexts. International Journal of Law and Psychiatry, 24, 23-42.