David Buss, Psychologist, University of Texas, conducted numerous studies investigating the underlying motives and circumstances of murders, from those of serial killers to the perfectly friendly next-door neighbor who one day commits murder.
He examined FBI files of more than 429,729 homicide case files; 13,670 of which were cases in which a husband killed his wife.
One study conducted by Dr. Buss on normal individuals not convicted of any serious crime revealed that 90% of husbands had at least once entertained a fantasy of killing their wife. Among the men who entertained thoughts of murdering their mates, 54 percent were triggered by the woman ending the relationship.
Of course, most people dont carry out fantasies of murder, due to restraints of morality and the fear of being caught and sent to prison for a very long time. However, when fantasy does become reality, it often catches everyone by surprise.
Though we may like to think that murderers are either pathological misfits or hardened criminals, he added,
the vast majority of murders are committed by people who, until the day they kill, seem perfectly normal.
The most dangerous time for a woman to be murdered by her husband is when she is making plans to leave the marriage (85% of all wife murders).
Just when women feel as though they have successfully escaped a bad marriage is precisely the time when their lives are most in danger, he added. It is likely that the key danger is not the length of time per se but, rather, when the man realizes she will never return to him.
http://www.utexas.edu/features/2005/murder/