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The act of unlawfully killing another human being unintentionally.
Most unintentional killings are not murder but involuntary manslaughter. The absence of the element of intent is the key distinguishing factor between voluntary and involuntary manslaughter. In most states involuntary manslaughter results from an improper use of reasonable care or skill while performing a legal act, or while committing an act that is unlawful but not felonious.
Many states do not define involuntary manslaughter, or define it vaguely in common-law terms. Some jurisdictions describe the amount of Negligence necessary to constitute manslaughter with terms such as criminal negligence, gross negligence, and culpable negligence. The only certainty that can be attached to these terms is that they require more than the ordinary negligence standard in a civil case. With this approach the state does not have to prove that the defendant was aware of the risk.
Other jurisdictions apply more subjective tests, such as "reckless" or "wanton," to describe the amount of negligence needed to constitute involuntary manslaughter. In this approach the defendant must have personally appreciated a risk and then chosen to take it anyway.
There are two types of involuntary manslaughter statutes: criminally negligent manslaughter and unlawful act manslaughter. Criminally negligent manslaughter occurs when death results from a high degree of negligence or recklessness. Modern criminal codes generally require a consciousness of risk and under some codes the absence of this element makes the offense a less serious Homicide.
An omission to act or a failure to perform a duty constitutes criminally negligent manslaughter. The existence of the duty is essential. Since the law does not recognize that an ordinary person has a duty to aid or rescue another in distress, a death resulting from an ordinary person's failure to act is not manslaughter. On the other hand, an omission by someone who has a duty, such as a failure to attempt to save a drowning person by a lifeguard, might constitute involuntary manslaughter.
In many jurisdictions death that results from the operation of a vehicle in a criminally negligent manner is punishable as a separate offense. Usually it is considered a less severe offense than involuntary manslaughter. These jurisdictions usually call the offense reckless homicide, negligent homicide, or vehicular homicide. One reason for this lesser offense is the reluctance of juries to convict automobile drivers of manslaughter.
Unlawful act manslaughter occurs when someone causes a death while committing or attempting to commit an unlawful act, usually a misdemeanor. Some states distinguish between conduct that is malum in se (bad in itself) and conduct that is malum prohibitum (bad because it is prohibited by law). Conduct that is malum in se is based on common-law definitions of crime; for example, an Assault and Battery could be classified as malum in se. Acts that are made illegal by legislation—for example, reckless driving—are malum prohibitum. In states that use this distinction, an act must be malum in se to constitute manslaughter. If an act is malum prohibitum, it is not manslaughter unless the person who committed it could have foreseen that death would be a direct result of the act.
In other states this distinction is not made. If death results from an unlawful act, the person who committed the act may be prosecuted for involuntary manslaughter even if the act was malum prohibitum. Courts will uphold unlawful act manslaughter where the statute was intended to prevent injury to another person.