Measuring the effects of the guilty but mentally Ill (GBMI) verdict

We studied effects of guilty but mentally ill (GBMI) legislation on use of the insanity defense in Georgia using data on all defendants entering an insanity plea before (1976–1981) and after (1982–1985) the introduction of the GBMI verdict. In contrast to earlier studies, our results indicated that GBMI did decrease the likelihood of an insanity verdict and affected the composition of those found not guilty by reason of insanity. Defendants pleading insanity and found GBMI were typically white males with a serious mental disorder, charged with murder or robbery in which an unrelated female victim was involved. The data also indicated that defendants who pleaded insanity and were found GBMI received harsher sentences than their guilty counterparts. We conclude that the GBMI verdict will make the insanity plea a less appealing option for mentally ill defendants.