Voluntary manslaughter cases where the defendant may have an intent to cause death or serious injury, but the potential liability for murder is mitigated by the circumstances and state of mind. The most common example is the so-called heat of passion killing, such as where the defendant is provoked into a loss of control by unexpectedly finding a spouse in the arms of a lover or witnessing an attack against his or her child.
There have been two types of voluntary manslaughter recognized in law, although they are so closely related and in many cases indistinguishable that many jurisdictions do not differentiate between them.
Provocation. This is a killing caused by an event or situation which would probably cause a reasonable person to lose self-control and kill.
Heat of Passion. In this situation, the actions of another cause the defendant to act in the heat of the moment and without reflection. This falls under the provocation heading.
Diminished Responsibility is another defence to murder that will negate the charge down to voluntary manslaughter. An abnormality of the mind that causes the defendant to not know what he is doing at the time of the killing.
Involuntary manslaughter, sometimes called criminally negligent homicide in the United States or culpable homicide in Scotland, occurs where there is no intention to kill or cause serious injury but death is due to recklessness or criminal negligence.
Negligence consists of conduct by an individual which is not reasonable -- that is, the individual did not act with the care and caution of a reasonable person in similar circumstances. This "reasonable person" is fictitious, of course, but reflects the standard of conduct which society wishes to impose. Violation of this standard may lead to civil liability for the consequences of the negligent behavior.
Negligence rises to the level of criminal negligence where the conduct reaches a higher degree of carelessness or inattention, perhaps to the point of indifference.
Recklessness or willful blindness is defined as a wanton disregard for the known dangers of a particular situation. An example of this would be throwing a brick off a bridge onto vehicular traffic below. There exists no intent to kill, consequently a resulting death may not be considered murder. However, the conduct is probably reckless, sometimes used interchangeably with criminally negligent, which may subject him to prosecution for involuntary manslaughter: the individual was aware of the risk of danger to others and willfuly disregarded it.
In many jurisdictions, such as in California, if the unintentional conduct amounts to such gross negligence as to amount to a willful or depraved indifference to human life, the mens rea may be considered to constitute malice. In such a case, the offense may be murder, often characterized as second degree murder.
In some jurisdictions, such as Victoria, recklessness is sufficient mens rea to justify a conviction for murder.