Psychosis and the Risk of Stranger Homicides

Ilkka Ojansuu, Markku Lähteenvuo, Jari Tiihonen, Martti Lehti, Hanna Putkonen

Research output: Contribution to journalArticleScientificpeer-review


Psychosis increases the risk of committing homicide, but it remains unclear whether it also affects victim selection. Individual cases of stranger homicide elicit a lot of public attention and outrage, even though evidence of their incidence is scarce. Methods: Forensic psychiatric reports of 389 patients who had committed homicide in Finland during 1980-2014 were examined to determine the relationship between the offender and the victim. The stranger homicide incidence derived from perpetrators with psychosis was compared to a comparative incidence derived from a group of perpetrators without psychosis (other mental disorders were not excluded) over the time frame 2003-2014. Stranger homicide incidence rates were calculated using Finnish population averages of the study years, assuming a Poisson distribution and reported as per 100 000 person-years among potential victims in the Finnish general population. Results: Three hundred and eighty nine patients with psychosis had committed 414 homicides, with 40 complete stranger victims and 15 victims known for less than 24 h. Complete stranger homicide incidence committed by individuals with psychosis was 0.022 per 100 000 person-years and 0.13 for individuals without psychosis. When also including victims known for<24 h, the incidence was 0.031 for individuals with psychosis and 0.28 for individuals without psychosis per 100 000 person-years. Discussion: Nine out of ten stranger homicides are committed by individuals without psychosis. However, on the basis of a 3.1% prevalence of psychotic disorders in Finland, individuals with psychosis have about a 3- to 5-fold risk of committing stranger homicides as compared to individuals without psychosis.

Original languageEnglish
Article numbersgac021
JournalSchizophrenia bulletin open
Issue number1
Number of pages6
Publication statusPublished - Feb 2022
MoE publication typeA1 Journal article-refereed

Bibliographical note

Funding Information:
The study was funded by the Finnish Ministry of Social Affairs and Health, through the developmental fund for Niuvanniemi Hospital. IO has received a personal grant from the Finnish Medical Foundation, and ML has received personal grants from the Finnish Medical Foundation, Emil Aaltonen Foundation, and the Finnish Cultural Foundation. The funders were not involved in the conduct of the study or in the collection, management, analysis, or interpretation of the data.

Funding Information:
We thank Hannu Kautiainen (Medcare Oy) for his work with statistical analyses and Aija Räsänen for secretarial assistance. IO has received research funding from the Finnish Medical Foundation, honoraria from Ratiopharm, consultancy fees from Camurus, and has attended a congress trip provided by MSD. ML is an owner and board member of Genomi Solutions Ltd and Nursie Health Ltd, and has received honoraria, study grants, or other financial support from Sunovion, Orion Pharma, Janssen-Cilag, Otsuka Pharma, Lundbeck, Medscape, the Finnish Medical Foundation, Emil Aaltonen Foundation, and the Finnish Cultural Foundation. JT has participated in research projects funded by grants from Janssen-Cilag and Eli Lilly to his employing institution. He reports lecture fees from Eli Lilly, Janssen-Cilag, Lundbeck, and Otsuka; consultancy fees from EMA (European Medicines Agency), Fimea (Finnish Medicines Agency), and Lundbeck; He also notes receipt of grants from the Stanley Foundation and the Sigrid Jusélius Foundation. MLe and HP report no conflicts of interest.

Fields of Science

  • epidemiology
  • homicide
  • psychosis
  • stranger
  • 3124 Neurology and psychiatry

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