In the personality of the poisoner, the investigator will probably find some of the following traits: an absolute defiance of legal authority; a refusal to accept any moral basis for life; killing to gain emotionally or materially; an unfortunate married life for the offender; a childhood in which the poisoner has either been spoiled by parents or reared in an unhappy home; a tendency to turn victim into an object with no feelings; an abnormal life with wife, children, or home; feeling that they have failed to make any kind if impression on life; a tendency to be daydreamers and fantasists; a touch of an artistic temperament; possible connection with the medical world as physicians, nurses, pharmacists, dentists, other health care workers, or laboratory workers with familiar with chemicals; possession of vanity in thinking they can not be discovered, in that they carefully calculate the odds and believe they can get away with crime; a limited mind without sympathy; and weak, cowardly and avaricious temperament.
One sees in the childish personality of the poisoner an immature desire for their own way, and a dreamy, romantic disposition. There seems to be something in the poisoners that keeps them permanently immature; they never seem to grow up. They try to make the world obey their will by cheating it in minor ways, and thereby stealing what it refuses to give them.
"Criminal Poisoning: An Investigational Guide for Law Enforcement ...", John H. Trestrail