Under the law, murder is a more grave crime as compared to involuntary manslaughter. The main difference under the law is that murder involves a more conscious element in its commission as compared to involuntary manslaughter. It must be remembered that there are different ways that a crime can be committed with each degree depending on the consciousness and depravity of the act. The criminal intent, or mens rea, is the foremost consideration when comparing murder and manslaughter.
Murder presupposes that there is malice and criminal intent in the commission of the crime. The deliberate thought of committing the crime as shown by the acts of the criminal betrays the criminal intent of the perpetrator. This premeditation shows a greater degree of depravity in the acts of the criminal and thus is given a greater penalty. An example of this would be the act of a criminal in carefully planning a crime and carrying it out; buying the necessary weapons to commit the crime and making the proper arrangements in order to prevent the discovery of the crime.
Involuntary manslaughter, on the other hand, is a totally different matter. It does not involve the mens rea but rather is absent of malice yet still results in the death of a person. There is no determinable intent to kill or commit the resulting crime.
This can result from an act of self-defense. Constructive manslaughter is also an involuntary form of manslaughter that describes the death of a person through non-intentional means or through acts that are considered as preater intentionem (resulting act is greater than that intended) or abberatio ictus (mistake in blow). In these two cases, there is no clear intent to commit the crime or cause the death of another but a death resulted nevertheless but not due to any intent on the perpetrator.