Guilty But Mentally Ill is a verdict stating that defendants are guilty of committing a crime but are also suffering from a mental illness that should be treated during their imprisonment. Guilty With Diminished Capacity is a legal defense argument that states that because of limitations posed by mental dysfunctioning, a defendant could not have intended to commit a particular crime and thus should be convicted of a lesser crime.
Comer, R. J. (2010). Abnormal psychology (8th ed.). New York, NY: Worth Publishers.