The killing of cousins and siblings-in-law has been examined as part of ‘relative killings’ in prior research. However, they have not been disaggregated and examined in their own right. A content analysis of a major Korean newspaper (Chosun Ilbo) and sentencing verdicts from regional trial courts of original jurisdiction in Korea was conducted. This paper examines the offence characteristics in cousin and siblings-in-law killings. Cousin and siblings-in-law killings made up 4% of 682 family homicides. The victims and offenders were primarily men who used edged weapons to kill one another during the course of arguments. Women appeared as offenders and victims in the early period (1948–1962) while they appeared primarily as victims in the latter period (2013–2023). The data suggest a shift in the age structure of victims and putative motivations across time. The average age of victims and offenders increased by 20 years; the character of violence also shifted from confrontational homicides to killings in the context of domestic disputes between relatives' spouses.