Do "murder", "manslaughter" and "homicide" have different legal definitions? Or are they just terms referring to the same act used in different jurisdictions?
Murder is intentional and premeditated killing. Manslaughter is also criminal killing but is not murder, because it is not premeditated e.g. someone comes home and discovers the spouse in bed with someone else, and "kills." That's voluntary manslaughter. Homicide is killing, criminal or not, so "self defense" or accidental killing is homicide. All murder and manslaughter is homicide, but not all homicide is manslaughter or murder.
There's another category of involuntary manslaughter.
Example: You are driving in a residential neighborhood at a "safe" speed of 10 mph. A small child rushes under your car, you can't swerve, and kill the child. That's accidental killing, not "manslaughter."
Example: You are driving in the same neighborhood at 30 mph. That's well above the 15 mph considered "safe." If you hit a child, you will now be charged with criminal involuntary manslaughter, or homicide, because of your "reckless disregard" for safety.
Example: You are driving at 10 mph, but are DUI, which slows your reflexes. If you now hit a child while under the influence of alcohol, that's criminal involuntary manslaughter.
The answer is going to depend on what jurisdiction you're talking about. But I can give you some general principles that apply, in most cases, in the U.S. at least.
"Homicide" is a general term for the killing of one person by another. If someone died, and another person caused it, it's homicide.
"Murder" and "manslaughter" are specific crimes, usually now defined by state criminal statutes. The specifics are going to differ from state to state, but in general, murder is the more serious crime and carries a more serious punishment.
So if a person dies at another person's hand, it is a homicide, and it may also be murder or manslaughter.
The way the law distinguishes between murder and manslaughter usually has to do with the killer's mental state. For example, a state with three homicide offenses might break them down like this:
- Murder: "I killed him because I wanted to steal his wallet."
- Voluntary manslaughter: "I killed him because I just found out he was sleeping with my wife."
- Involuntary manslaughter/negligent homicide: "I didn't mean to kill him, but I was drunk and didn't see the stop sign."
These homicide offenses will then be further subdivided into degrees based on aggravating or mitigating factors. For instance, in some states there is a very limited definition for first degree murder, which may be the only offense that allows the death penalty (example: murder of a police officer, murder while serving a life sentence).