What does manslaughter mean, and how is it different from murder?

The jury in the murder trial of former BART Police Officer Johannes Mehserler returned a verdict of involuntary manslaughter today. How can a person cause the death of another without the act being considered a murder?

In the universe of legalese, words can perform in unusual ways. Manslaughter, simply defined, is “the unlawful killing of a human being without malice.” American law designates two types of manslaughter, voluntary and involuntary.

Voluntary manslaughter roughly means that accused intended to hurt or possibly kill the victim, but extenuating circumstances influenced the situation. This classification is used if the accused was provoked by the victim, or if the accused was mentally compromised when committing the crime.

Involuntary manslaughter generally applies where death is the unintentional consequence of the actions of the accused. Wikipedia uses this example: “If a person throws a brick off a bridge into vehicular traffic below,” and a person were to die as a result.

U.S. law also distinguishes between types of murder. First degree murder is defined by the planning (premeditation) of the act, whereas second degree is considered a “crime of passion,” the accused killing out of emotional strain or impulse.