List of mass murderers and spree killers by number of victims
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This is a partial list of individual mass murderers and spree killers organised by the number of victims, further divided into several subsections. The intention behind this list is not to provide a complete overview of incidents, otherwise it would grow out of proportions very soon, but concentrates on cases that stick out by their sheer number of victims.
As there's often conflicting information about the number of dead and injured, which do not include the perpetrators themselves, in cases of uncertainty a range is given.

In colloquial language the term mass murderer is commonly used to describe anyone who intentionally caused, directly or indirectly, the death of many people. This rather vague definition is applied on states, governments, organziations, groups or persons who order genocides, massacres, war crimes, terrorist acts or similar deeds and their perpetrators, as well as individuals who do not act on behalf of higher institutions, but out of their own personal motivations, like school shooters, spree killers, arsonists and even serial killers.

The focus of this list, lies on the latter group, individuals, with the restriction to persons who are directly responsible for each death, meaning targeting every single person separately. This excludes arsons, bombings, poisonings or other forms of mass murder where the perpetrator has no direct control on who will fall victim to his crime, but includes terrorist acts by lone gunmen which are later claimed to be perpetrated in the name of an organization, e.g. the Mercaz HaRav massacre.
Furthermore serial killers are also left out, because their modus operandi of killing, as well as their motivations are significantly different from common mass murderers and spree killers.

According to the USA Bureau of Justice Statistics mass murder is defined as "the murder of four or more victims at one location, within one event."^{citation needed}
In regards of this list, this definition is insufficient though, as it does not explain further what can be seen as "one location", e.g. it leaves unclear if a neighbourhood is viewed as one location or as many, counting every house separately. It also does not explain if a whole shooting spree, stretching over hours or maybe days can be seen as one big event, or just as a sequence of smaller events.
Further this definition does not include those who did not kill four or more, but set out with the intention to murder as many people as possible, e.g. Denis Lortie who killed three and therefore would not be a mass murderer, according to the above definition, but the 13 people he left injured certainly qualify his rampage as attempted mass murder.

Thus, this list will contain every case with one or both of the following features:

• Cases with six or more dead (excluding the perpetrator)
• Cases with a double digit number of victims (dead plus injured)

For more comprehensive information which cases are included in every subsection, see there.

Generally, the deeds of individual mass murderers have in common that the attacks on their victims come in rather short succession without much time to "cool down" and their rampages rarely last longer than a few hours. Also, many of them do not survive their crimes themselves, either because they finish them by committing suicide, or get killed. Only very few get away uncaught.

Besides that, many distinctions can be made within the mass murderer category, though the transition from one group to the other can be smooth. For one there are mass murderers whose crimes are more or less spontaneous, like the case of Carl Brown, often involving alcohol abuse beforehand. On the other hand there are mass murderers who make extensive planning, sometimes months in advance before they put them into practice. Examples for this would be the Columbine massacre or the Virginia Tech massacre.
Then there are cases where the victims are very carefully chosen, either because of their relation to the perpetrator or their relation to each other. Those in this group are more likely to take great care to really kill their victims, but also often end up in killing everyone at hand. Typical examples would be family murders, attacks on ethnic or religious groups, or the notorious "hit list". Other mass murderers do not have a certain target and kill people just at random without caring whom they are hitting, often simply moving from one victim to the next, after it was hit.
Another distinction would be that some stick to one location, like George Hennard, while others keep moving.

The motivations behind mass murders can be many. From simple robbery, financial and social problems or religious fundamentalism and racism, to outright hatred towards the whole world, the motives cover a broad range, with revenge being maybe the most predominant of them all. Many mass murderers seem to suffer from depression or narcissism and are often stating to have been victims of bullying, mobbing or other forms of humiliation.^[1]

Mass murders

This category contains incidents that occurred at one rather confined place - typical examples would be mosques and restaurants, as well as trains and planes - or somehow separate places that form some kind of compound, like mall and parking lot. Also included are incidents that happened in the open, where the perpetrator showed very limited movement, e.g. in the case of Ami Popper. Further all cases with uncertainty about the vastness of the crime scene are added here.
This section does not include school massacres or workplace killings, which form their own categories, or murders related to robberies with more than one offender.

Killing sprees

The U.S. Bureau of Justice Statistics defines a spree killing as "killings at two or more locations with almost no time break between murders."^[119]

The classic form of the spree killer is "a killer on the run", who rarely kills more than one or two on every occasion, while trying to evade capture - examples would be Charles Starkweather or Andrew Cunanan - but in recent times the term is more and more applied on any mass murderer who kills at two or more locations, though instead of the former their intention is rarely not to get caught, but to kill, even at the cost of their own life. This means that the classic spree killer is rarely a mass murderer in the common sense, nonetheless both forms can be found in this category, as well as mass murderers who are strolling the streets, like Barend Strydom or Howard Unruh. ^[120]

Workplace killings

People killing their (former) co-workers; also includes soldiers killing their comrades.