There are around six or seven household homicide-suicides a year in Switzerland. For the first time, risk factors have been examined in a Swiss national cohort study, by a group headed by Radoslaw Panczak and Professor Matthias Egger of the Institute of Social and Preventive Medicine at the University of Bern. The results, published in the journal PLoS ONE in January, show that frequency of these events did not change during this period.

In homicides followed by the perpetrator's suicide, there is a clear division of gender roles. In over 93% of the cases examined, perpetrators were male; 84% of the victims were female. In 75% of these incidents, a man murdered his wife; in another 8%, he also killed one or more children. The age distribution of the perpetrators peaks at 45 and 75. "Besides classic homicide-suicides motivated by jealousy, there are also perpetrators in the older generation who kill their seriously ill wives out of despair or an inability to cope," says Egger. Male perpetrators were more frequently divorced than married and, and more often without religious affiliation than Catholic. The presence of children in the household, native language, and urban or rural environment appeared to have no effect.

The study also showed no connection between social class and the incidence of household homicide-suicides. According to the researchers, education and the profession had no influence, either. Nationality did not play a role, with a single exception: foreigners on a temporary residency permit were more frequently perpetrators. "Other stressful life situations, such as divorces or cramped living conditions also increase the risk," said Professor Egger.

Firearms almost always used

The weapon used in over 85% of cases was a firearm. The researchers were unable to determine if these were military weapons because this data is not included in the mortality statistics. According to Egger, however, international studies show a strong correlation between the availability of firearms and the number of homicide-suicides in a country. Switzerland has more of these events, in proportion to the population, than do other European nations. Professor Egger is convinced that "homicide-suicides could be prevented by limiting access to weapons."

This was the first national cohort on the topic of homicide-suicides at population level, and it analysed a total of seventy-three incidents, in which 158 people were killed. The project is part of the Swiss National Cohort (http://www.swissnationalcohort.ch) and was supported by the Swiss National Science Foundation and the Swiss Federal Statistical Office.

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