They aren't mutually exclusive at all -- it's just that the psychoanalytical (or behaviorist or neurological) explanation is superfluous. True or false, it simply doesn't help.
Carrol ===========
"In recent years several neurological conditions have been introduced into criminal trials as part ofthe insanity defense, for example, epilepsy, premenstrual syndrome, hypoglycemia, post-traumatic syndrome, and psychopathy. An unusual case involving the impact of alcohol on the brain is told in 'The Crocodile Man'. A young college student, male, attacked and almost killed two women in a bar one evening after ingesting a small amount of beer. The father of the defendant, who happened to be a prominent biochemist a northeastern university, felt that there was a biochemical defect in his son's brain that caused this sensitivity to alcohol. After months of research, a defect in the liver enzyme system that processes alcohol was found.
"One of the most interesting uses of neurological testimony in a criminal trial occurred in the trial of John Hinckley Jr., the man who shot Pres. Ronald Reagan in 1981. The government tried to show that Hinckley was rational [that he knew right from wrong] at the time of the crime because he had written to actress Jodie Foster, he had purchased a gun, and he had tracked the president for several months. Government psychiatrists also testified that Hinckley had a mood disorder.
"The defense psychiatrists testified that Hinckley was schizophrenic or perhaps borderline personality. The most interesting aspect of the case, and one totally ignored by the Low, Jeffries, and Bonnie discussion of the case, was the testimony of a young biological psychiatrist from Harvard University Medical School by the name of David Bear. Bear attempted to introduce into the trial a CAT scan taken of Hinckley's brain at Duke University Medical Center where Hinckley had been sent for a psychiatric evaluation. The CAT scan revealed that the ventricles of Hinckley's brain were abnormally enlarged with major portions of the brain missing. The judge ruled that the CAT could not be admissible as evidence. At that point a major argument occurred between Bear and the judge, and Bear refused to appear as an expert witness unless he was allowed to introduce into the trial the scientific evidence he used in coming to his conclusions about the status of Hinckley's brain. The judge then allowed the CAT scan to be introduced as evidence." [C Wray Jeffery, 'The Medicalization of Crime' in "The Neurotransmitter Revolution ed. by Roger Masters & Michael McGuire Southern University Press, 1994]
for percolations and non-linearity,
Ian