Most people use the words “murder” and “homicide” interchangeably, but they are not the same. Although murder and homicide are both used to describe the act of killing another human being, the circumstances surrounding the charges are different.
The easiest way to describe the differences between murder and homicide is that homicide is the killing of another human being, while murder requires the intent to kill another human being. Homicide can be used to describe any death where another person is at fault, but there are mitigating circumstances that can influence the charge of homicide. When someone is convicted of murder, however, they are not only convicted of a homicide, but also the malicious intent to kill.
In the United States, we have terms like “justifiable homicide” and “non-criminal homicide” that are used to describe acts of homicide where there is no “mens rea” involved. The U.S. requires that the prosecution in a criminal trial prove both actus reus and mens rea in a criminal crime; the former translates as “guilty mind” and the latter refers to “guilty act”. Actus reus is simply the proof that a defendant committed a criminal act, while mens rea is a little more complicated. In order to prove mens rea, the prosecution must show that the defendant either had an intent to commit the crime or acted with criminal negligence.
With this in mind, you must understand that homicide is not always illegal, while murder is always illegal. For example, judicial homicide involves the use of deadly force by a law enforcement officer who must kill in order to save his life or the lives of others. Although judicial homicide is usually investigated by the Internal Affairs Bureau (IAB), criminal charges are not brought against the officer unless there is evidence that deadly force was unnecessary.
Another example of justifiable homicide is when a private citizen kills to protect himself, his family or valuable possessions (such as in the case of a robbery). Although it is quite dangerous to ever commit homicide, the law recognizes circumstances of self defense.
Criminal homicide can either be classified as murder or manslaughter. Typically, a murder charge implies an intent to kill, while manslaughter implies criminal negligence. For example, a drunk driver who gets into an accident and kills someone else might be charged with vehicular manslaughter, while someone who shoots his enemy in the chest would be charged with murder.
Intent can often be difficult to prove, especially if there is little in the way of direct evidence. Most law enforcement officers are taught to assume intent until it can be proven otherwise during the course of an investigation. If there is even a slight possibility of intent (i.e. murder), the police will investigate it. Criminal negligence is a little bit easier to prove since it usually involves carelessness or the consumption of a controlled substance.