The labels describe crimes. Victims and evidence decide cases.

What makes a series hard to identify?

The FBI’s 2008 monograph on serial murder points to the victims and the agencies. A series involving high-risk victims in multiple jurisdictions is much more difficult to identify, and the lack of communication between agencies impedes linking cases. Most typologies, it says, may not be helpful in identifying an offender.^2,9,10,11

Classification describes crimes. It does not name the person who committed them. The FBI’s 2008 monograph says most typologies are too cumbersome to be used during an active serial murder investigation, and “may not be helpful in identifying an offender.”^2,9

Identifying a series is easier in rapidly developing, high-profile cases involving low-risk victims, which are reported on discovery, the monograph says.¹⁰ It is much more difficult when high-risk victims are spread across multiple jurisdictions, and the lack of communication between agencies and differing records management systems impede the linkage of cases.^10,11

Some serial killers stop. The FBI lists the belief that serial killers cannot stop killing as a myth, and says some stop altogether before being caught.¹² Evidence closed three of Samuel Little’s cases more than two decades later: arrested on a narcotics charge in 2012, he was matched by DNA to three unsolved Los Angeles homicides from 1987 and 1989, and convicted in 2014.^13,14

What counts as serial murder?

The FBI defines serial murder as the unlawful killing of two or more victims by the same offender or offenders, in separate events.¹ Federal law draws its own lines. The 1998 statute lets the FBI investigate serial killings, a series of three or more killings, when the agency with jurisdiction asks; a 2013 law defines mass killings as three or more killings in a single incident.^2,3

Madison Mogen, Kaylee Goncalves, Xana Kernodle and Ethan Chapin were killed in an off-campus home in Moscow, Idaho, in the early morning hours of November 13, 2022.^4,5 By these definitions, that is a mass killing, not a series.

Do the organized and disorganized types hold up?

The split came from the FBI. A 1980 article in the FBI Law Enforcement Bulletin named two types: the organized nonsocial and the disorganized asocial personality.⁶ In 1985 the Bulletin reported interviews with 36 convicted sexual murderers, 25 of them serial murderers, whom the FBI’s technique sorted into 24 organized and 12 disorganized.⁷

In 2004, Canter, Alison, Alison and Wentink tested the split on 100 murders committed by 100 U.S. serial killers and found no distinct subsets of offense characteristics reflecting it.⁸ Organized features were typical of most serial killings; disorganized features were much rarer and did not form a distinct type.⁸

Who gets counted?

Not every victim. Many deaths tied to Samuel Little were originally ruled overdoses or accidental or undetermined deaths, the FBI says. A third of the 48 women then known as Gary Ridgway’s victims had never been reported missing, were absent from police databases, or were never identified. Robert Piest’s disappearance was under police investigation the same day.^{15,16,17,18,19}

In Steven Egger’s definition, the less-dead are the majority of serial murder victims, who belong to marginalized groups and are generally not missed when they are gone.²⁰ Many deaths tied to Samuel Little were originally ruled overdoses or attributed to accidental or undetermined causes.¹⁵ A third of the 48 women then known as Gary Ridgway’s victims had never been reported missing, were absent from police missing-persons databases, or were never identified.^16,17,19

Robert Piest, 15, went missing from the Des Plaines pharmacy where he worked on the evening of December 11, 1978, and police were investigating the report that same day.^18,21 The Illinois Supreme Court’s 1984 opinion records a warrant to search John Wayne Gacy’s home two days later.¹⁸