His killing campaign unfolded across nearly two years and two countries, making him one of the most geographically mobile serial killers of the 1920s — a period when coordinated interstate law enforcement barely existed. He targeted landladies responding to room-for-rent advertisements, a method that gave him access to victims while evading suspicion for months. The breadth of his movements, from the West Coast through the Midwest and into Canada, repeatedly outpaced local investigations until Canadian authorities finally closed the net.

Roubal operated across the early 1990s in Czechoslovakia, killing victims he encountered through ordinary transactions — taxi rides, classified ads, car rentals — then taking their vehicles and property almost immediately afterward. The pattern of acquisition was consistent enough that possession of a dead man's car became, more than once, the first sign to the outside world that something was wrong. His convictions, eventually secured after a procedurally troubled trial, covered five murders, though several further disappearances connected to him were never resolved due to the absence of remains.

Known within Cosa Nostra as "The Pope," Greco held authority over the Sicilian Mafia's ruling commission during one of its most violent periods, the early 1980s, when internal purges and open warfare produced casualties in the hundreds. His influence derived less from direct violence than from the organizational standing he commanded, which made him central to decisions that others carried out. He died in prison, convicted of multiple murders, having never publicly acknowledged the weight of what was decided in his presence.