2.1 The Rise of Stranger Homicides and the Decline of "Crimes of Passion"
Decades ago, homicide was predominantly a "crime of passion" involving family members or close acquaintances. These cases were inherently easier to solve because the victim-offender relationship was already established, providing a clear starting point for investigators. However, the criminological landscape has changed dramatically. A study of homicide trends in San Diego between 1970 and 1980 revealed a marked increase in stranger-to-stranger homicides. While the proportion of acquaintance homicides declined from 67% in 1970 to 34% in 1980, the rate of felony homicides, such as those related to robbery, increased significantly.
This trend has continued, and its effect on clearance rates is profound. While the share of homicides with an "unknown" victim-offender relationship has hovered between 30% and 40% for the past four decades, this share surged to over 50% in 2020 and 2022. This shift creates a difficult challenge for investigators, as they are now faced with a majority of cases where the most basic information—who committed the crime and why—is absent at the outset.
2.2 The Increasing Prevalence of Felony Homicides and Gun Violence
The rise of stranger-to-stranger homicides is directly linked to an increase in felony-related killings. The share of homicides with an "unknown" circumstance doubled from 22% in 1985 to 43% in 2022. The shift toward felony homicides, particularly prominent during the crack cocaine epidemic, has moved murder "out of a domestic setting into the street". In cases where circumstances were reported, about 15% of homicides were committed during the course of another felony, such as robbery or drug trafficking.
Furthermore, the nature of the weapon used has also changed. In the 1960s, guns accounted for approximately 50% of homicides; today, the national average is 80%. In Chicago, this figure is even higher, at over 90%. Homicides involving firearms are statistically more difficult to solve , as they are often committed in public settings where witnesses are less likely to cooperate and the perpetrator is a stranger.
A deeper analysis of these trends reveals a self-reinforcing cycle of "unknowns" and low clearance rates. The shift toward a more impersonal form of homicide, characterized by stranger-to-stranger violence and an increase in gun use, makes the initial victim-offender relationship and motive inherently less clear. When a case lacks a clear starting point, it becomes exponentially more difficult for law enforcement to identify a suspect and gather the necessary evidence, which in turn lowers the clearance rate. This accumulation of unsolved cases with "unknown" circumstances and relationships further entrenches the problem, making it harder for law enforcement to determine a clear picture of violent crime in a given jurisdiction. The problem is not merely about police effectiveness but about the changing criminal landscape, which presents a fundamentally more challenging set of circumstances for investigators.
