In the journalism business, we have to choose our words very carefully, because words that may seem like synonyms can be very different.

That's why when a person is killed by another, we write that police are investigating a homicide, rather than a murder.

Merriam Webster's online dictionary defines "homicide" as the killing of one human being by another.

Meanwhile, the dictionary defines "murder" as the verb meaning "to kill (a human being) unlawfully and with premeditated malice."

Therefore police won't use the word murder until they have determined a killing was criminal, said Det. Eric Buschow of the Ventura County Sheriff's Department's Thousand Oaks office.

Police will generally be investigating a "homicide," but they may use the word murder once a suspect is identified or arrested. A suspect would generally be wanted on suspicion of murder or arrested on suspicion of murder.

Homicide can be deemed murder, or it can be deemed justified, manslaughter, etc. (Manslaughter is defined by Merriam Webster's as "the unlawful killing of a human being without express or implied malice.")

As a reporter, there's an additional level of complication I have to be aware of in cases like these: Even though the manner in which a crime might be described to me by law enforcement or other sources might vary, I have to make sure that I write things in a consistent way.

 For that reason, newspapers and other media outlets have defined "styles" for how they write certain things.

The main standard we use is a guide called the Associated Press Stylebook. It has entries on everything from academic titles to zero-base budgeting.

The entry for homicide reads like this:

"homicide, murder, manslaughter
Homicide is a legal term for slaying or killing.
Murder is malicious, premeditated homicide. Some states define certain homicides as murder if the killing occurs in the course of armed robbery, rape, etc.
Manslaughter is homicide without malice or premeditation.
A person should not be described as a murderer until convicted of the charge.
Unless authorities say premeditation was obvious, do not say that a victim was murdered until someone has been convicted in court. Instead, say that a victim was killed or slain."

I've highlighted the second to last sentence of the entry because it shows that AP style is actually more restrictive than the dictionary definition. Even if authorities are ready to call a killing a murder, we might not use that word if they have not made it clear that the act was premeditated.