A homicide is any situation in which one person causes the death of another. The word describes an event, not a verdict: some homicides are crimes like murder or manslaughter, some are lawful acts like self-defense or a court-ordered execution, and some sit in a gray zone until investigators and prosecutors sort them out. So the short answer to what a homicide is: a human killing a human, with the legal consequences decided separately.
Homicide on a Death Certificate Is Not a Criminal Charge
When a medical examiner or coroner investigates a death, they assign one of five manners: natural, accident, suicide, homicide, or undetermined.1CDC. Medical Examiners’ and Coroners’ Handbook on Death Registration A homicide classification means another person caused the death. It does not mean a crime occurred. The examiner documents how someone died; whether anyone broke the law is a separate question for police, prosecutors, and courts.
This confuses people constantly. News reports say a death has been “ruled a homicide” and readers assume charges are imminent. In reality, the ruling is just a starting point. A police shooting shows up as a homicide on the death certificate even when the officer acted lawfully. The ruling triggers an investigation; the legal system then decides, independently, whether anyone faces criminal liability.
Lawful Homicides
Not every killing is a crime. The law recognizes several circumstances where causing someone’s death carries no criminal penalty. These generally fall into the older common-law categories of justifiable and excusable homicide, though most modern statutes treat them the same way and impose no punishment for either.
Self-Defense and Defense of Others
The most common lawful homicide involves self-defense. To qualify, you generally must show you reasonably believed you faced an imminent threat of death or serious physical harm, and that deadly force was necessary to stop it. The danger has to be immediate. A threat that might materialize next week will not justify lethal force today.
Whether you must retreat before using deadly force depends on your state. At least 31 states have stand-your-ground laws that remove any duty to retreat when you are somewhere you have a legal right to be.2National Conference of State Legislatures. Self Defense and Stand Your Ground The remaining states generally require retreat if it can be done safely, with one major exception: the castle doctrine. Under castle doctrine rules, you have no obligation to retreat when someone unlawfully enters your home. Nearly every state recognizes some version of this, even those that otherwise require retreat in public.
Police Use of Deadly Force
Officers can lawfully use deadly force when they reasonably believe a person poses an imminent danger of death or serious injury to the officer or someone else. The governing standard comes from the Supreme Court’s decision in Graham v. Connor, which requires courts to judge the officer’s actions from the perspective of a reasonable officer at the scene, not with hindsight. Deadly force cannot be used solely to stop a fleeing suspect, and firing at moving vehicles is prohibited outside narrow conditions.3U.S. Department of Justice. Department of Justice Policy on Use of Force
Executions
A lawful execution carried out under a valid court order is also a justifiable homicide. The death certificate lists the manner of death as homicide, but the act is authorized by law and carries no criminal liability for anyone involved in carrying it out.
Murder
Murder is the most serious form of criminal homicide. Under federal law, it is the unlawful killing of a human being with malice aforethought.4Office of the Law Revision Counsel. 18 USC 1111 – Murder The phrase sounds archaic, but it means something specific: the killer either intended to kill or cause serious harm, or acted with such extreme recklessness that the law treats their state of mind as the equivalent of intent. Murder splits into two degrees, and the difference drives sentencing.
First-Degree Murder
First-degree murder covers killings that were planned in advance. The prosecution must show the defendant had time to reflect on what they were about to do and went ahead. Evidence of planning might include prior threats, buying a weapon, or lying in wait. Under federal law, first-degree murder is punishable by death or life in prison.4Office of the Law Revision Counsel. 18 USC 1111 – Murder
First-degree murder also includes felony murder: a death that occurs during the commission of certain dangerous crimes, even if the killing was unintentional. Under federal law, the qualifying felonies include arson, burglary, robbery, kidnapping, and sexual abuse, among others.5Congress.gov. Federal Homicide: From Murder to Manslaughter If two people commit an armed robbery and one of them shoots the store clerk, both can be charged with first-degree murder, including the robber who never touched the gun. State lists vary but tend to include the same core offenses.
Second-Degree Murder
Second-degree murder is the catch-all for intentional killings that were not planned ahead of time. A bar fight where someone grabs a bottle and strikes a fatal blow fits: no advance planning, but clear intent to cause serious harm in the moment. Federal law punishes second-degree murder with any term of years up to life imprisonment.4Office of the Law Revision Counsel. 18 USC 1111 – Murder
This category also covers “depraved heart” murder, meaning killings caused by conduct so reckless that it shows a complete disregard for human life. The classic example is firing a gun into a crowded room. The shooter may not have aimed at anyone, but the behavior is so dangerous that the law treats it as morally equivalent to intentional killing.5Congress.gov. Federal Homicide: From Murder to Manslaughter
Manslaughter
Manslaughter covers unlawful killings committed without malice. Federal law splits it into voluntary and involuntary, with the dividing line being the killer’s state of mind.6Office of the Law Revision Counsel. 18 USC 1112 – Manslaughter
Voluntary Manslaughter
Voluntary manslaughter is sometimes called a “heat of passion” killing. It applies when someone who would otherwise be guilty of murder was provoked so severely that a reasonable person could have lost self-control and acted the same way. A lot of courtroom fighting happens here, because a successful provocation argument can be the difference between a life sentence and a far shorter one.
Two things have to be true. The defendant must have actually experienced an overwhelming emotional reaction, and the provocation must be the kind of thing that would push a reasonable person past the breaking point, not just something that made the defendant angry. Timing matters: if enough time passed for the defendant to cool off, the defense fails and the charge stays at murder. Federal law caps voluntary manslaughter at 15 years in prison.6Office of the Law Revision Counsel. 18 USC 1112 – Manslaughter
Involuntary Manslaughter
Involuntary manslaughter covers deaths caused by reckless or unlawful conduct where the person did not intend to kill. Federal law defines it as a death occurring during the commission of a non-felony crime, or during a lawful activity performed without reasonable caution.6Office of the Law Revision Counsel. 18 USC 1112 – Manslaughter Reckless driving that kills a pedestrian is a standard example. The federal penalty is up to 8 years, though state penalties vary.
Negligent Homicide and Vehicular Homicide
Negligent homicide sits a step below manslaughter. The defendant did not intend to hurt anyone and may not have consciously recognized the risk, but a reasonable person in their position would have. The focus is on what the defendant should have known. This charge commonly comes up in workplace deaths where safety protocols were ignored, or traffic cases where inattention caused a fatal crash.
Many states have carved out a separate offense called vehicular homicide for deaths caused by impaired or reckless driving. Before these statutes, prosecutors had to shoehorn driving deaths into involuntary manslaughter, which did not always work cleanly. Vehicular homicide laws often tie directly to specific traffic offenses like DUI or reckless driving. Penalties range widely by state, from under a year in some jurisdictions to life imprisonment in Washington, and typically increase sharply when alcohol or drugs were involved.
What the Prosecution Has to Prove About Causation
Identifying the person who killed someone is only part of a homicide case. The government also has to prove that the defendant’s actions legally caused the death, and criminal causation is more demanding than people assume.
The first test is straightforward: “but for” the defendant’s conduct, would the victim have died? If someone poisons a drink and the victim dies from the poison, the answer is yes. The law also requires proximate cause, meaning a direct enough link between the act and the death that it is fair to hold the defendant responsible. An unforeseeable event that breaks the chain can cut off criminal liability. If a defendant injures someone and the ambulance taking the victim to the hospital crashes and kills them, the original attacker may not be liable for the death.
A single death can have more than one proximate cause. Two people who independently contribute to a fatal outcome can both face homicide charges.
Civil Wrongful Death Suits Run on a Separate Track
A criminal case is not the only legal consequence of a homicide. The victim’s family can file a wrongful death lawsuit against the person responsible, and the two cases operate independently. The biggest difference is the burden of proof. Criminal prosecution requires proof beyond a reasonable doubt. A wrongful death plaintiff only needs to show it is more likely than not that the defendant caused the death, a standard called preponderance of the evidence.
That gap explains how someone can be acquitted of murder and still lose a wrongful death suit over the same killing. The O.J. Simpson case is the famous example, but it happens regularly in cases that never make the news. State laws decide who can file, usually a surviving spouse, children, or the representative of the estate. Damages can include the income the victim would have earned, funeral costs, and compensation for the family’s emotional loss.