Under federal law, mass murder is any incident in which three or more people are killed, a threshold set by the Investigative Assistance for Violent Crimes Act of 2012 and codified at 28 U.S.C. § 530C.1LII / Legal Information Institute. Definition: Mass Killings From 28 USC 530C(b)(1) That number is the only codified federal line. But “mass murder” is not itself a criminal charge. Prosecutors file separate counts of murder for each victim and often add federal charges on top depending on the motive, the weapon, and where the killings happened.
The Statutory Threshold
Congress added the definition to the U.S. Code after the Sandy Hook Elementary School shooting. The statute defines a mass killing as “3 or more killings in a single incident.”2GovInfo. Investigative Assistance for Violent Crimes Act of 2012 It specifies no weapon, no setting, and no victim profile. The practical trigger built into the law is federal investigative assistance: once the threshold is met, the Attorney General can offer federal resources to state and local law enforcement responding to the incident.1LII / Legal Information Institute. Definition: Mass Killings From 28 USC 530C(b)(1)
Before 2012, the FBI and most researchers used a threshold of four or more victims killed. That older figure still appears in criminology literature and news coverage, which is why the number varies by source. For federal legal purposes, three is the controlling figure.
How It Differs From Serial and Spree Killings
The distinction is timing. A mass murder happens in one continuous episode, whether that lasts minutes or hours. There is no return to ordinary life between killings.
Serial murder stretches across weeks, months, or years. The FBI defines it as the killing of two or more victims in separate events with a gap between each one that lets the offender resume daily routines.3Federal Bureau of Investigation. Serial Killers, Part 1: The FBI’s Role Takes Shape That gap, often called a cooling-off period, is the defining feature.
Spree killing sits between the two. A spree killer strikes at multiple locations over a short period without any cooling-off break, such as killing at one location and then driving to another and killing again within hours.4Office of Justice Programs. Multiple Murder: A Review The FBI has largely moved away from treating spree killing as a rigid category because the line between spree, mass, and serial often blurs in real cases. For prosecution, the label matters less than the evidence of what the defendant did and intended.
How Mass Murder Is Charged
No federal or state code contains a crime called “mass murder.” When a mass killing occurs, prosecutors file an individual murder charge for each victim. Six deaths produce six counts of homicide, each with its own potential sentence.
Within federal jurisdiction, murder is charged under 18 U.S.C. § 1111. First-degree murder, meaning any killing that is premeditated or committed during certain other felonies, carries a mandatory sentence of either death or life in prison.5Office of the Law Revision Counsel. 18 USC 1111 – Murder No lesser sentence exists for that conviction. Second-degree murder allows any term of years up to life.
Most mass murder cases are still prosecuted in state court, because the overwhelming majority of homicides fall under state jurisdiction. State first-degree murder statutes typically carry mandatory minimums ranging from 20 years to life without parole. In either system, a defendant convicted of multiple first-degree murder counts almost always faces the rest of their life in prison.
When Federal Jurisdiction Attaches
Federal prosecutors can bring charges alongside state charges, or instead of them, in several situations. The most common routes are hate crimes, firearms offenses, attacks on federal property, and terrorism-related statutes.
Hate Crimes
The Matthew Shepard and James Byrd Jr. Hate Crimes Prevention Act makes it a federal offense to cause bodily injury or death because of a victim’s race, color, religion, national origin, gender, sexual orientation, gender identity, or disability. When death results, each count carries a maximum sentence of life in prison.6Office of the Law Revision Counsel. 18 USC 249 – Hate Crime Acts Federal prosecutors used this statute to bring 27 counts against the man accused of the 2022 Buffalo supermarket shooting, covering both the victims killed and those he attempted to kill.7United States Department of Justice. Federal Grand Jury Indicts Accused Tops Shooter on Federal Hate Crimes and Firearms Charges in Buffalo, New York
Firearms Offenses
Federal firearms counts are among the most powerful add-ons in mass shooting cases because they carry mandatory minimum sentences that must run consecutively to any other sentence. Under 18 U.S.C. § 924(c), using or carrying a firearm during a crime of violence adds at least five years. Discharging the firearm raises the minimum to ten. A short-barreled rifle, shotgun, or semiautomatic assault weapon also triggers ten years, and a machine gun or destructive device brings a 30-year mandatory minimum.8Office of the Law Revision Counsel. 18 USC 924 – Penalties Those enhancements cannot run concurrently with the sentence for the underlying crime. With multiple victims, each count can carry its own consecutive firearms enhancement, which is how federal sentences in mass shooting cases reach hundreds of years before any murder count is counted.
Federal Property and Terrorism Statutes
Attacks on federal buildings, military installations, or other federal property fall within federal jurisdiction automatically. Where a killing involves support for a designated foreign terrorist organization, 18 U.S.C. § 2339B authorizes prosecution for providing material support, with a life sentence available when death results.9Office of the Law Revision Counsel. 18 USC 2339B – Providing Material Support or Resources to Designated Foreign Terrorist Organizations
Sentencing and the Federal Death Penalty
Mass murder cases are where the federal death penalty most often comes into play. Under 18 U.S.C. § 3592, one of the statutory aggravating factors that makes a defendant death-eligible is having “intentionally killed or attempted to kill more than one person in a single criminal episode.”10Office of the Law Revision Counsel. 18 USC 3592 – Mitigating and Aggravating Factors to Be Considered in Determining Whether a Sentence of Death Is Justified That language maps onto mass murder directly. Any mass killing prosecuted federally is death-eligible if the government chooses to seek that penalty.
Whether prosecutors actually pursue a death sentence is a separate decision shaped by Justice Department policy, the strength of the evidence, the defendant’s mental health history, and the position of victims’ families. Recent federal mass shooting prosecutions have produced both death sentences and negotiated pleas to life without parole.
When sentencing on multiple murder counts, each count is evaluated on its own. Murder counts are not grouped together the way some fraud or drug counts can be. The court looks at each killing individually, which typically produces the highest offense level and consecutive sentences.11USSC. Approaches in Multiple Counts
Mass Murder Is Not Automatically Domestic Terrorism
Not every mass killing qualifies as terrorism. Federal law defines domestic terrorism as violent acts that appear intended to intimidate a civilian population, influence government policy through coercion, or affect government conduct through mass destruction, assassination, or kidnapping, occurring primarily within U.S. territory and in violation of federal or state criminal law.12Office of the Law Revision Counsel. 18 USC 2331 – Definitions
A disgruntled employee who kills coworkers at a warehouse has committed mass murder but likely has not committed domestic terrorism, absent evidence of a broader political or ideological motive. A person who attacks a house of worship to frighten a religious community out of a city sits closer to the terrorism threshold because the intent reaches past the immediate victims.
There is also no standalone federal charge called domestic terrorism. The label triggers investigative authorities and can influence charging decisions, but prosecutors still rely on existing statutes covering murder, hate crimes, firearms, and weapons of mass destruction. The designation carries weight at the investigative stage, through access to federal intelligence resources and interagency coordination, and at sentencing, where a finding of premeditated terrorism can function as an aggravating factor.