Murder is defined as the unlawful killing of one human being by another with malice aforethought. For first degree murder there must be evidence of premeditation. The lesser charge of second degree murder involves killing with malice aforethought but without premeditation. Voluntary manslaughter is the intentional killing of a person without malice aforethought under circumstances that mitigate but do not excuse or justify the killing. Generally, such a killing occurs when a defendant is moved by intense passion induced by adequate provocation. Courts have held that adequate provocation is shown when the accused or a close relative has been violently attacked by the deceased, during mutual combat unsought by the accused, and when the accused actually sees his/her spouse committing adultery and kills one or both parties involved. Another partial defense which, like the provocation defense, does not excuse or justify the taking of human life, is diminished capacity. It provides a compromise between guilt and exculpation and serves to mitigate punishment. This defense allows evidence of mental incapacity to disprove or negate evidence of premeditation or malice. Unintentional homicide includes involuntary manslaughter and criminal negligence. Involuntary manslaughter is the killing of another without malice and unintentionally but in the doing of some unlawful act not a felony nor naturally tending to cause death or great bodily harm. The law also recognizes that a homicide may be excusable under circumstances where the accused was legally insane at the time of the killing, was involuntarily intoxicated, or was under the influence of automatism, a state of unconsciousness which is not caused by mental disease or defect but by some external factor. Another defense is justifiable homicide, which consists of killing in self defense, in defense of third parties, and of necessity. The most complete defense is one in which the defendant denies having killed the victim. In making such a defense, the crucial interplay of circumstantial and direct evidence plays an important role.