Operating in rural Álava across two distinct periods, Garayo is considered one of Spain's earliest documented serial killers, and his case drew enough contemporary attention to produce a dedicated monograph before he was even executed. His crimes followed a pattern of escalation — beginning with the killing of women he had hired, then broadening to attacks on strangers encountered in the countryside. The written record left by Ricardo Becerro de Bengoa, based on prison visits, gives the case an unusually direct documentary quality for its era.

Southard's alleged crimes unfolded quietly across a series of marriages, each ending in a death that drew little suspicion until the pattern became too consistent to ignore. Operating in rural Idaho in the early twentieth century, she is suspected of poisoning at least four husbands, a brother-in-law, and her own daughter — extracting arsenic from household flypaper and collecting life insurance payouts in the aftermath. The domestic setting and the ordinariness of her methods were central to how long she evaded detection.

Over more than a decade, Chikatilo operated across multiple Soviet republics while evading a law enforcement system poorly equipped — and at times ideologically resistant — to acknowledge that such crimes could occur within the USSR. His case became one of the most extensive serial murder investigations in Soviet history, complicated by wrongful convictions of other men in the interim. The eventual prosecution and trial brought rare public visibility to crimes that Soviet authorities had long suppressed from official acknowledgment.

A former storehouse helper who rose to become chief executioner at one of the Nazi occupation's most active killing sites, Weiss oversaw more than a thousand executions within the walls of Pankrác prison between 1943 and 1945. His postwar life in West Germany drew no apparent accountability, and his later attempt to claim a Czech government pension — framing his role as that of a public servant — stands as a measure of how thoroughly he had rationalized his work.

Solonik rose through the violent hierarchies of post-Soviet organized crime to become one of the most feared contract killers of the 1990s, accumulating a string of high-profile assassinations tied to Russian mob power struggles. His ability to escape custody twice — including from one of Russia's most secure facilities — added to a reputation that made him a near-mythic figure within the underworld. He died under disputed circumstances in Greece in 1997, but the details of his final years remain murky enough that the full account of his career has never been definitively closed.

Over twelve years, Chikatilo carried out a series of attacks across three Soviet republics that investigators struggled for years to connect and attribute to a single perpetrator — a failure that allowed the killings to continue long after the pattern had become apparent. His case drew scrutiny not only for the scale of the crimes but for the systemic breakdowns in Soviet law enforcement that enabled his evasion, including the wrongful prosecution of others during the investigation.