The legal definition of homicide is simply the killing of one human being by another. The word itself carries no accusation. It describes a fact, not a crime. Whether a particular homicide is murder, manslaughter, lawful self-defense, or a tragic accident depends entirely on the circumstances surrounding the death and the mental state of the person who caused it.
Why Homicide Doesn’t Mean Crime
Medical examiners, police, and courts all use “homicide” as a neutral term. When a medical examiner rules a death a homicide, that is a factual finding that another person’s actions caused the death. It is not a legal conclusion that anyone should be charged with a crime.
Medical examiners classify every death into one of five categories: natural, accident, suicide, homicide, or undetermined. A homicide ruling on a death certificate means the examiner found that another person’s actions caused the death, intentionally or not. The legal system then decides separately whether those actions were criminal, justified, or excusable. A prosecutor can look at a death the examiner labeled “homicide” and decline to file charges because the killing was lawful.
So a homicide finding and a criminal charge are two different things. Every criminal homicide is a homicide, but not every homicide is a crime.
Murder
A homicide becomes murder when the killer acted with what federal law calls malice aforethought. The term is older than it is literal. Malice aforethought does not require hatred or long-held planning. It means the person either intended to kill, intended to cause serious bodily harm, acted with extreme recklessness showing indifference to human life, or killed someone during the commission of a dangerous felony.1Office of the Law Revision Counsel. 18 U.S.C. 1111 – Murder
Federal law splits murder into two degrees. First-degree murder covers killings that were premeditated and deliberate, along with killings committed during certain dangerous felonies such as arson, kidnapping, burglary, robbery, sexual abuse, or child abuse. Everything else that qualifies as murder is second degree. First-degree murder carries death or life in prison. Second-degree murder carries any term of years up to life.1Office of the Law Revision Counsel. 18 U.S.C. 1111 – Murder
That felony category is called the felony murder rule, and it catches people off guard. If two people rob a convenience store and the cashier dies of a heart attack during the robbery, both robbers can face first-degree murder charges even though neither one pulled a trigger or intended anyone to die. The prosecution only needs to show that a death occurred during a qualifying felony. Most states have their own version of the rule, and the triggering felonies vary, but the core principle is the same: commit a dangerous felony where someone dies, and that death is charged as a murder.
Manslaughter
Manslaughter is an unlawful killing without malice. Federal law recognizes two kinds.2Office of the Law Revision Counsel. 18 U.S.C. 1112 – Manslaughter
Voluntary manslaughter is a killing committed in the heat of passion or during a sudden fight. The classic example is a person who walks in on a spouse’s affair and kills the other party in a rage. The intent to harm was there in the moment, but the law treats it as less serious than murder because adequate provocation reduced the person’s ability to think clearly. The federal penalty is up to 15 years in prison.2Office of the Law Revision Counsel. 18 U.S.C. 1112 – Manslaughter
Involuntary manslaughter is a death caused by criminal negligence or by committing an unlawful act that falls short of a felony. A contractor who ignores safety codes and a worker dies. A person who fires a gun into the air during a celebration and the bullet kills someone on the way down. Nobody planned for anyone to die, but reckless or negligent behavior caused it. The federal penalty is up to eight years in prison.2Office of the Law Revision Counsel. 18 U.S.C. 1112 – Manslaughter
Many states also treat vehicular homicide as its own offense, covering deaths caused by reckless or impaired driving. Some states fold it into involuntary manslaughter. Others have separate statutes with their own penalty ranges. Drunk or drugged driving that causes a fatal crash is the most common scenario, with excessive speeding and street racing not far behind.
When Killing Is Lawful
Some homicides are not crimes at all. The law separates these into two categories.
Justifiable homicide covers killings the law expressly permits. Self-defense is the most familiar example. If you reasonably believe someone is about to kill you or cause you serious bodily harm, you can use lethal force to stop them. The word “reasonably” does a lot of work. Courts ask whether a typical person in your position would have perceived the same level of threat, not simply whether you were afraid. Most states also require that the threat be imminent, so a vague future threat does not justify killing someone today. Justifiable homicide also includes executions carried out under a lawful death sentence and lethal force used by police officers to stop an immediate threat to life.
Excusable homicide is narrower. It covers deaths that happen by genuine accident while someone is doing something lawful with ordinary caution. A tree surgeon who follows every safety protocol but whose falling branch strikes and kills a passerby fits here. There was no unlawful intent, no recklessness, and no way to foresee the death. These are classified as homicides because one person’s actions caused another’s death, but no criminal liability attaches.
Proving a Homicide
To tie a death to a particular person as a homicide, prosecutors have to show causation. There are two kinds, and both have to hold up.
The first is actual cause, often called “but-for” causation. Would the victim have died when and how they did without the suspect’s actions? If the answer is no, actual cause is established. A gunshot victim would not have died but for the shooter pulling the trigger.
The second is proximate cause, which asks whether the death was a foreseeable consequence of the person’s actions. This is where homicide cases get complicated. If someone throws a punch, the victim stumbles into the street, and a bus hits them, was that death a foreseeable result of the punch? Courts look at the full chain of events. When an unforeseeable event breaks that chain, such as a stranger deliberately shoving the stumbling victim into traffic, the intervening act may cut off the first attacker’s liability for the death. Defense attorneys regularly challenge proximate cause, arguing that something else, like the victim’s own choices or a medical error during treatment, was the real reason the victim died.
Unborn Victims Under Federal Law
A person who injures or kills an unborn child while committing certain federal crimes faces a separate offense for the harm to the child. The Unborn Victims of Violence Act defines a “child in utero” as a member of the species at any stage of development who is carried in the womb. The penalty matches whatever the person would have faced if the same injury had been inflicted on the mother.3Office of the Law Revision Counsel. 18 U.S.C. 1841 – Protection of Unborn Children
The federal law reaches only offenses under federal jurisdiction, such as crimes on federal property or against federal employees. It does not apply to abortion performed with the pregnant person’s consent or to medical treatment. Prosecutors do not have to prove the offender knew the victim was pregnant or intended to harm the unborn child. Roughly two-thirds of states have enacted their own fetal homicide laws, and the specifics vary widely.3Office of the Law Revision Counsel. 18 U.S.C. 1841 – Protection of Unborn Children
Time Limits for Charges
Murder has no statute of limitations under federal law. An indictment for any offense punishable by death can be brought at any time, no matter how many years have passed.4Office of the Law Revision Counsel. 18 U.S.C. 3281 – Capital Offenses Every state applies the same principle to murder.
Manslaughter is different. Because it is not a capital offense, time limits apply, usually three to six years, though some states set no limit for felony-level homicide of any kind. The practical result is that cold cases involving potential murder charges can be reopened decades later, while manslaughter investigations face more pressure to resolve quickly.
Civil Lawsuits After a Homicide
A homicide can produce both a criminal case and a civil lawsuit, and the two run on separate tracks. The victim’s family can file a wrongful death claim against the person responsible, seeking money damages for lost financial support, funeral costs, and emotional suffering. A criminal acquittal does not block a civil case, because the burden of proof is lower. In civil court the family has to show that the defendant more likely than not caused the death, rather than proving it beyond a reasonable doubt.
The O.J. Simpson case is the familiar example. A jury acquitted him of murder, and a civil jury later found him liable for the deaths and awarded the victims’ families tens of millions of dollars. Filing deadlines for wrongful death lawsuits are typically two to three years from the date of death depending on the state, and missing that window forfeits the claim.