A physician who turned medical knowledge into a means of killing, Palmer operated at a time when forensic toxicology was still in its infancy — a circumstance that likely allowed multiple deaths to go undetected before investigators closed in on him. The case against him centered on a single murder, but contemporaries and later historians suspected the toll was considerably higher, possibly including his wife and brother. His trial drew national attention and prompted reform to English venue law, as local bias made a fair hearing in Rugeley impossible.

The last of his five killings occurred on his twenty-sixth birthday, a detail that captures something of the compressed, years-long arc of violence he carried out across northern Italy. Operating in and around Bolzano between 1985 and 1992, he targeted women across different circumstances — a teenage student, prostitutes — with a consistency of method that led courts to convict him across all five cases despite his partial denials. Forensic experts disagreed sharply over his mental state, and two unrelated murders from the same period were never definitively linked to him, leaving the full scope of his actions uncertain.

A criminal history preceding his killings by decades, Dudnik had accumulated three rape convictions during the Soviet period before the collapse of that system left him free in independent Kazakhstan. His murders of at least three women in a short span around Vishnevka represent a late and lethal culmination of a long pattern of violent offending.

His role in the Gulf Cartel extended well beyond enforcer — as plaza boss across key Tamaulipas territories, he helped hold together a criminal organization during a period of sustained pressure from Mexican authorities. Mexican investigators credit him with triggering one of the most consequential fractures in recent cartel history: a 2010 killing he ordered set in motion the open rupture between the Gulf Cartel and Los Zetas, a split whose violence reshaped the security landscape of northeastern Mexico for years afterward.

His name first surfaced in the unsolved 2005 disappearance of American teenager Natalee Holloway, a case that drew years of international attention without resolution — until, nearly two decades later, he admitted to killing her in a legal proffer. In the intervening years, he murdered Stephany Flores Ramírez in a Lima hotel room on the five-year anniversary of Holloway's disappearance, attempted to extort Holloway's family by offering information about her remains, and continued trafficking cocaine from inside a Peruvian prison. The accumulation of offenses across multiple countries — murder, extortion, fraud, drug trafficking — reflects less a single act of violence than a sustained pattern of exploitation that stretched across continents and years.