The authors have declared that no competing interests exist.
Conceived and designed the experiments: RP, MZ, ME. Performed the experiments: RP, MZ, AS, ME. Analyzed the data: RP, MZ, ME. Contributed reagents/materials/analysis tools: RP, MZ, AS. Wrote the paper: RP, KT, MK, ME.
Homicide–suicides are rare but catastrophic events. This study examined the epidemiology of homicide-suicide in Switzerland.
The study identified homicide–suicide events 1991–2008 in persons from the same household in the Swiss National Cohort, which links census and mortality records. The analysis examined the association of the risk of dying in a homicide–suicide event with socio-demographic variables, measured at the individual-level, household composition variables and area-level variables. Proportional hazards regression models were calculated for male perpetrators and female victims. Results are presented as age-adjusted hazard ratios (HR) with 95% confidence intervals (95%CI).
The study identified 158 deaths from homicide–suicide events, including 85 murder victims (62 women, 4 men, 19 children and adolescents) and 68 male and 5 female perpetrators. The incidence was 3 events per million households and year. Firearms were the most prominent method for both homicides and suicides. The risk of perpetrating homicide-suicide was higher in divorced than in married men (HR 3.64; 95%CI 1.56–8.49), in foreigners without permanent residency compared to Swiss citizens (HR 3.95; 1.52–10.2), higher in men without religious affiliations than in Catholics (HR 2.23; 1.14–4.36) and higher in crowded households (HR 4.85; 1.72–13.6 comparing ≥2 with <1 persons/room). There was no association with education, occupation or nationality, the number of children, the language region or degree of urbanicity. Associations were similar for female victims.
This national longitudinal study shows that living conditions associated with psychological stress and lower levels of social support are associated with homicide-suicide events in Switzerland.
Violent deaths due to injuries and accidents contribute importantly to premature mortality and life-years lost. Defined as the homicide of one or several individuals followed by suicide of the perpetrator, homicide-suicide events, also referred to as ‘extended suicide’, ‘murder–suicide’ or ‘dyadic death’ represent a small but important segment of injury deaths
Homicide-suicide events generally include one perpetrator and one victim: the majority of perpetrators are men and most victims are women
Several authors have argued that the rate of homicide-suicide varies less between countries than the rate of homicide, such that homicide-suicide as a percentage of all homicides is negatively correlated with the rate of homicide
Previous studies of homicide-suicide events were generally based on case series and focused on forensic and criminological aspects of the events
We analysed the data from the SNC, which has been described in detail elsewhere
The census consisted of three questionnaires: one for the individual, a household questionnaire and a questionnaire on the building. Each person living in Switzerland at the time of census (or their legal representative) was obliged by law to complete the personal questionnaire. The household questionnaire, which covers the number of persons living in the household, including children and other relatives, is completed by the head of the household. The head of household is defined as the person economically responsible for the household. All questionnaires and a complete list of variables are available at
The events of interest were clusters of one or several homicides and one suicide that occurred within a household of at least two persons. We included households of married or cohabitating couples with or without children that were recorded in one or both of the 1990 or 2000 censuses. The analysis excluded individuals living in single person or single parent households, people living in institutions, and households of several adults sharing accommodation, for example students. Causes of death linked to the SNC were coded according to the eighth revision of the International Classification of Diseases, Injuries and Causes of Death (ICD-8) until 1994, and the 10th revision (ICD-10) thereafter. The analysis limited cases to deaths registered with the primary cause as defined by the codes:
953–958 for violent suicides; 960–968 for homicide (ICD-8);
X70– X82 for violent suicides; X91– X99 and Y00– Y09 for homicide (ICD-10).
Deaths had to occur in sequence, with the homicide or homicides occurring before the suicide. A maximum time window of 14 days between the two events was allowed.
We used demographic and socio–economic data at the level of the individual, data on the composition of households and crowding, and data on the characteristics of the area. At the individual level nationality was grouped into categories ‘Swiss’, ‘Other European’ and ‘Other or unknown’. Residence status was in four categories: ‘Swiss’, ‘Permanent residence permit’, ‘Annual/seasonal permit’ and ‘Other’. Reported religious affiliation was categorised into four groups: ‘Protestant’, ‘Catholic’, ‘No affiliation’ and ‘Other affiliation/unknown’. ‘No affiliation’ was an explicit response option in the census questionnaire. The analysis considered four categories of educational attainment (‘Compulsory schooling or less’, ‘Secondary’, ‘Tertiary’ and ‘Unknown’). Categories of socio–professional status classification were collapsed into 10 hierarchical groups reflecting the position and status of individuals in the labour market. At the level of the household we considered the number of adults living in the household (2 or >2 adults), the number of children (0, 1, ≥2 children) and the number of persons per room (combining bed and living rooms): <1, 1–<2 and ≥2. Finally, the study considered characteristics of the area of residence. The level of urbanisation was in three categories: ‘Urban, ‘Peri-urban’ and ‘Rural’ according to the classification of communities provided by the Swiss Federal Office of Statistics, and language region in three: ‘German’, ‘French’, and ‘Italian’.
The analysis used descriptive statistics to characterize the perpetrators and victims of homicide-suicide events. A Cox proportional hazard regression was used to examine associations of socio-demographic characteristics with the hazard of becoming a perpetrator (death by suicide) among the adult male Swiss population living in eligible households. Similarly - the hazard of becoming a victim (death by homicide) was modelled among the adult female Swiss population. The observation time started at the date of the earliest census the individual was recorded as a member of a household with two or more persons (December 4th 1990 or December 5th 2000) and ended at the date of death by homicide or suicide, the date of emigration or December 31st 2008, whichever came first. The study censored the time of observation on December 5th 2000 in individuals who lived in households with two or more persons in 1990 but were recorded as living in ineligible households or institutions in 2000.
Age-adjusted hazard ratios were obtained by using age as the time scale in the Cox proportional hazard models. Results were expressed as hazard ratios (HR) with 95% confidence intervals (CI). We obtained
The 1990 census included a total of 6,873,687 residents and the 2000 census 7,288,010 residents, for a combined total of 8,527,638 potentially eligible individuals. A total of 1,114,221 deaths were recorded in Switzerland between December 5th 1990 and December 31st 2008. Among these 1,052,619 (94.5%) deaths could be linked to a census record using probabilistic record linkage
We identified 73 homicide–suicide events involving 158 deaths. In 1991 and 2001, when ascertainment of events was near complete, there were six and seven events, respectively. The homicide-suicide offending rates per 100,000 were 0.09 and 0.10 and victimization rates 0.13 and 0.15 in 1991 and 2001 respectively. This translated into a rate per 1,000,000 eligible households of 3.01 in 1991 and 2.95 in 2001 (
Events | Victims | Total deaths | |||||
Murder victim | No. | % | No. | % | No. | % | |
|
|||||||
(n = 68) | Wife | 55 | 75.3 | 55 | 64.7 | 110 | 69.6 |
Wife and adolescent offspring | 5 | 6.8 | 15 | 17.6 | 20 | 12.7 | |
Wife and adolescent son | 1 | 1.4 | 2 | 2.4 | 3 | 1.9 | |
Adult son | 1 | 1.4 | 1 | 1.2 | 2 | 1.3 | |
Adolescent son | 2 | 2.7 | 2 | 2.4 | 4 | 2.5 | |
Adolescent daughter | 1 | 1.4 | 1 | 1.2 | 2 | 1.3 | |
Other adult male | 1 | 1.4 | 1 | 1.2 | 2 | 1.3 | |
Other adult female | 2 | 2.7 | 2 | 2.4 | 4 | 2.5 | |
|
|||||||
(n = 5) | Husband | 3 | 4.1 | 3 | 3.5 | 6 | 3.8 |
Adolescent son | 1 | 1.4 | 1 | 1.2 | 2 | 1.3 | |
Adolescent offspring | 1 | 1.4 | 2 | 2.4 | 3 | 1.9 | |
|
73 | 100 | 85 | 100 | 158 | 100 |
Comparing the socio-demographic characteristics of perpetrators and victims with the population at risk shows marked differences in the sex and age distribution: 68 of the perpetrators (93.2%) were male and 71 (83.5%) of the victims were female (
Homicide–suicide events in Swiss households 1991–2008.
|
|
|
|
|
||||
No. | % | No. | % | No. | % | |||
Total | 73 | 100.0 | 85 | 100.0 | 6,854,339 | 100.0 | ||
|
|
Male | 68 | 93.2 | 14 | 16.5 | 3,500,564 | 51.1 |
Female | 5 | 6.8 | 71 | 83.5 | 3,353,775 | 48.9 | ||
|
0–19 | 0 | 0.0 | 19 | 22.4 | 1,713,519 | 25.0 | |
20–29 | 4 | 5.5 | 6 | 7.1 | 8,48,182 | 12.4 | ||
30–39 | 13 | 17.8 | 20 | 23.5 | 1,085,815 | 15.8 | ||
40–49 | 17 | 23.3 | 11 | 12.9 | 984,770 | 14.4 | ||
50–59 | 13 | 17.8 | 7 | 8.2 | 877,223 | 12.8 | ||
60–69 | 8 | 11.0 | 9 | 10.6 | 641,112 | 9.4 | ||
70–79 | 14 | 19.2 | 9 | 10.6 | 483,609 | 7.1 | ||
80+ | 4 | 5.5 | 4 | 4.7 | 220,109 | 3.2 | ||
|
Single | 2 | 2.7 | 23 | 27.1 | 2,657,797 | 38.8 | |
|
Married | 65 | 89.0 | 58 | 68.2 | 3,991,694 | 58.2 | |
Widowed | 0 | 0.0 | 1 | 1.2 | 67,378 | 1.0 | ||
Divorced | 6 | 8.2 | 3 | 3.5 | 137,470 | 2.0 | ||
|
Switzerland | 61 | 83.6 | 74 | 87.1 | 5,407,953 | 78.9 | |
Rest of Europe | 12 | 16.4 | 11 | 12.9 | 1,292,792 | 18.9 | ||
Other countries/unknown | 0 | 0.0 | 0 | 0.0 | 153,594 | 2.2 | ||
|
Swiss | 61 | 83.6 | 74 | 87.1 | 5,407,953 | 78.9 | |
|
Permanent residence | 7 | 9.6 | 8 | 9.4 | 1,038,269 | 15.2 | |
Short-term residence permit | 5 | 6.9 | 3 | 3.5 | 338,723 | 4.9 | ||
Other | – | – | – | – | 69,394 | 1.0 | ||
|
Protestants | 25 | 34.2 | 34 | 40.0 | 2,504,114 | 36.5 | |
Catholics | 28 | 38.4 | 33 | 38.8 | 3,003,618 | 43.8 | ||
No religious affiliation | 14 | 19.2 | 14 | 16.5 | 645,216 | 9.4 | ||
Other/unknown | 6 | 8.2 | 4 | 4.7 | 701,391 | 10.2 | ||
|
Compulsory education or less | 17 | 23.3 | 23 | 27.1 | 1,692,062 | 24.7 | |
Secondary | 37 | 50.7 | 38 | 44.7 | 2,661,270 | 38.8 | ||
Tertiary | 18 | 24.7 | 5 | 5.9 | 939,798 | 13.7 | ||
Unknown | 1 | 1.4 | 3 | 3.5 | 157,696 | 2.3 | ||
School age or younger | 0 | 0.0 | 16 | 18.8 | 1,403,513 | 20.5 | ||
|
Top management | 1 | 1.4 | 1 | 1.2 | 68,046 | 1.0 | |
Middle management | 2 | 2.7 | 2 | 2.4 | 261,991 | 3.8 | ||
Lower management | 4 | 5.5 | 6 | 7.1 | 530,751 | 7.7 | ||
Independent professions | 9 | 12.3 | 5 | 5.9 | 355,893 | 5.2 | ||
Skilled non-manual labour | 6 | 8.2 | 7 | 8.2 | 634,239 | 9.3 | ||
Skilled manual labour | 10 | 13.7 | 0 | 0.0 | 302,654 | 4.4 | ||
Unskilled manual labour | 4 | 5.5 | 7 | 8.2 | 516,012 | 7.5 | ||
Not classified | 10 | 13.7 | 3 | 3.5 | 709,298 | 10.3 | ||
Unemployed | 3 | 4.1 | 2 | 2.4 | 120,631 | 1.8 | ||
Not in paid employment | 24 | 32.9 | 36 | 42.4 | 1,951,310 | 28.5 | ||
In compulsory education | 0 | 0.0 | 16 | 18.8 | 1,403,514 | 20.5 | ||
|
|
2 | 70 | 95.9 | 82 | 96.5 | 6,414,873 | 93.6 |
>2 | 3 | 4.1 | 3 | 3.5 | 439,466 | 6.4 | ||
|
0 | 37 | 50.7 | 37 | 43.5 | 2,296,537 | 33.5 | |
1 | 12 | 16.4 | 12 | 14.1 | 1,391,698 | 20.3 | ||
> = 2 | 24 | 32.9 | 36 | 42.4 | 3,166,104 | 46.2 | ||
|
<1 | 44 | 60.3 | 51 | 60.0 | 4,29,8374 | 62.7 | |
1–<2 | 25 | 34.2 | 30 | 35.3 | 2,386,802 | 34.8 | ||
> = 2 | 4 | 5.5 | 4 | 4.7 | 169,163 | 2.5 | ||
|
|
German | 54 | 74.0 | 62 | 72.9 | 4,960,396 | 72.4 |
French | 15 | 20.5 | 17 | 20.0 | 1,599,605 | 23.3 | ||
Italian | 4 | 5.5 | 6 | 7.1 | 294,338 | 4.3 | ||
|
Urban | 22 | 30.1 | 23 | 27.1 | 1,758,448 | 25.7 | |
Peri-urban | 30 | 41.1 | 35 | 41.2 | 316,4160 | 46.2 | ||
Rural | 21 | 28.8 | 27 | 31.8 | 1,931,731 | 28.2 |
The proportion of married and divorced individuals was higher among both perpetrators and victims compared to the population at risk (
The Cox regression analysis was based on 2,624,839 men living in an eligible household, 35.9 million person-years of follow-up, and 68 events of men committing homicide-suicide. The small number of women perpetrators (n = 5) precluded analyses in women. The risk of committing homicide-suicide was increased in 30–49 year olds compared to younger men, and again increased in men aged 70 and above (
|
|
|
|
|
|
|
|
20–29 | 0.50 | (0.16–1.60) | 0.03 |
30–39 | 1.00 | – | |||
40–49 | 1.37 | (0.62–3.06) | |||
50–59 | 1.25 | (0.55–2.86) | |||
60–69 | 1.09 | (0.43–2.77) | |||
70–79 | 2.87 | (1.27–6.46) | |||
80+ | 2.26 | (0.71–7.22) | |||
|
Single | 0.43 | (0.10–1.88) | 0.02 | |
|
Married | 1.00 | – | ||
Widowed | – | – | |||
Divorced | 3.64 | (1.56–8.49) | |||
|
Switzerland | 1.00 | – | 0.15 | |
Rest of Europe | 1.22 | (0.65–2.31) | |||
Other countries/unknown | – | – | |||
|
Swiss | 1.00 | – | 0.03 | |
Permanent residence permit | 0.78 | (0.35–1.73) | |||
Annual or seasonal residence permit | 3.95 | (1.52–10.2) | |||
|
Protestants | 0.99 | (0.56–1.74) | 0.12 | |
Catholics | 1.00 | – | |||
No religious affiliation | 2.23 | (1.14–4.36) | |||
Other/unknown | 1.40 | (0.57–3.43) | |||
|
Compulsory education or less | 1.24 | (0.68–2.27) | 0.84 | |
Secondary | 1.00 | – | |||
Tertiary | 0.90 | (0.50–1.62) | |||
Unknown | 1.18 | (0.16–8.68) | |||
|
Top management | 0.72 | (0.08–6.45) | 0.18 | |
Middle management | 0.39 | (0.07–2.16) | |||
Lower management | 0.49 | (0.12–1.97) | |||
Independent professions | 1.10 | (0.33–3.66) | |||
Skilled non-manual labour | 1.00 | – | |||
Skilled manual labour | 2.15 | (0.67–6.84) | |||
Unskilled manual labour | 1.09 | (0.27–4.38) | |||
Not classified | 1.33 | (0.42–4.27) | |||
Unemployed | 2.53 | (0.46–13.8) | |||
Not in paid employment | 0.73 | (0.20–2.63) | |||
|
|
2 | 1.00 | – | 0.74 |
>2 | 0.83 | (0.26, 2.64) | |||
|
0 | 1.00 | – | 0.58 | |
1 | 0.98 | (0.48–2.04) | |||
> = 2 | 1.36 | (0.70–2.65) | |||
|
<1 | 1.00 | – | 0.01 | |
|
1–<2 | 2.00 | (1.17–3.43) | ||
> = 2 | 4.85 | (1.72–13.6) | |||
|
|
German | 1.00 | – | 0.71 |
|
French | 0.82 | (0.45–1.51) | ||
Italian | 1.26 | (0.46–3.50) | |||
|
Urban | 1.00 | – | 0.41 | |
Peri-urban | 0.68 | (0.39–1.21) | |||
Rural | 0.86 | (0.47–1.58) |
Hazard ratios adjusted for age from Cox regression models based on 2′624′839 men older than 18 years living in eligible households in Switzerland.
This analysis was based on 2,515,961 women living in eligible households, 35.1 million person-years of follow-up and 62 women killed in homicide-suicide events. The small number of male victims (n = 14) precluded analyses in males. The risk of dying in homicide-suicides was increased in women aged 30–39 years and women aged 80 years and older compared to other women (
|
|
|
|
|
|
|
|
20–29 | 0.36 | (0.14–0.98) | 0.050 |
30–39 | 1.00 | – | |||
40–49 | 0.46 | (0.21–1.02) | |||
50–59 | 0.41 | (0.17–0.97) | |||
60–69 | 0.74 | (0.34–1.64) | |||
70–79 | 1.13 | (0.51–2.50) | |||
80+ | 1.48 | (0.50–4.36) | |||
|
Single | 1.03 | (0.35–3.10) | 0.70 | |
|
Married | 1.00 | – | ||
Widowed | 0.63 | (0.08–4.69) | |||
Divorced | 2.04 | (0.64–6.57) | |||
|
Switzerland | 1.00 | – | 0.42 | |
Rest of Europe | 1.04 | (0.49–2.21) | |||
Other countries/unknown | – | – | |||
|
Swiss | 1.00 | – | 0.87 | |
Permanent residence | 0.93 | (0.39–2.17) | |||
Short-term residence permit | 1.14 | (0.27–4.80) | |||
|
Protestants | 1.63 | (0.91–2.92) | 0.02 | |
Catholics | 1.00 | – | |||
No religious affiliation | 3.29 | (1.56–6.95) | |||
Other/unknown | 0.95 | (0.28–3.20) | |||
|
Compulsory education or less | 0.88 | (0.49–1.55) | 0.48 | |
Secondary | 1.00 | – | |||
Tertiary | 0.75 | (0.29–1.93) | |||
Unknown | 2.46 | (0.75–8.06) | |||
|
Top management | 4.50 | (0.55–36.5) | 0.17 | |
Middle management | 0.92 | (0.11–7.49) | |||
Lower management | 1.22 | (0.36–4.16) | |||
Independent professions | 2.65 | (0.84–8.39) | |||
Skilled non-manual labour | 1.00 | – | |||
Skilled manual labour | – | – | |||
Unskilled manual labour | 1.69 | (0.56–5.04) | |||
Not classified | 0.33 | (0.07–1.58) | |||
Unemployed | 1.89 | (0.39–9.08) | |||
Not in paid employment | 1.17 | (0.47–2.93) | |||
|
|
2 | 1.00 | – | 0.71 |
>2 | 0.81 | (0.25–2.59) | |||
|
0 | 1.00 | – | 0.59 | |
1 | 0.67 | (0.30–1.52) | |||
> = 2 | 0.96 | (0.48–1.92) | |||
|
<1 | 1.00 | – | 0.07 | |
1–<2 | 1.66 | (0.94–2.94) | |||
> = 2 | 3.63 | (1.11–11.8) | |||
|
|
German | 1.00 | – | 0.80 |
French | 0.81 | (0.43–1.53) | |||
Italian | 1.02 | (0.32–3.28) | |||
|
Urban | 1.00 | – | 0.71 | |
Peri-urban | 0.82 | (0.45–1.51) | |||
Rural | 1.03 | (0.54–1.96) |
Hazard ratios adjusted for age from Cox regression models based on 2′515′961 women older than 18 years living in eligible households in Switzerland.
The availability of information on all individuals living in Switzerland at the time of the census as well as on the composition of their households, combined with the linked mortality data, made it possible to identify homicide-suicide events that took place in households of two adults with or without children. We identified 73 such events, with a total of 158 deaths, during the period 1991–2008. The study showed that the perpetrators were predominantly men while the victims were women, confirming data from numerous case series
The Swiss homicide rate of 0.9 per 100,000 is one of the lowest among European countries and has remained relatively stable for the last 20 years
This is the first nation-wide cohort study of homicide-suicide. It allowed possible predictors of homicide-suicide events to be examined at the level of the individual, household and area: the Swiss censuses 1990 and 2000 included comprehensive data on demographic and socio-economic characteristic of residents, the composition of households and the geographical coordinates of buildings. Some of these variables were associated with the risk of committing a homicide-suicide act among men, or the risk of being killed in such an event in women. Among men, the risk was increased in divorcees and in foreigners without permanent residency in Switzerland. The risk was also increased in overcrowded households with two or more persons per room. Other studies have found that overcrowding increases the risk of violence, generally, and the risk of violence against women, in particular
These associations reflect situations and living conditions that are often associated with general psychological stress and intimate partner strain. Sociological and criminological theories have repeatedly linked psychological stress and life pressures with violence. In 1938 Merton put forward what has become known as ‘strain theory’: by putting strain on some members of society, social structures will make it more likely for some to commit crimes than for others
Interestingly, both in male perpetrators and female victims the risk was higher in individuals without religious affiliation, compared to Catholics. Women with no religious affiliation may on average be less amenable to authority structures (including patriarchy) and less bound by traditional relationship roles, than Catholic and Protestant women: the woman leaving the relationship is often the trigger for the escalation of violence
Factors unrelated to risk are also worth noting. In particular, current study found no evidence that homicide-suicide was associated with education or occupation, two variables that measure important components of socio-economic position (SEP)
Homicide-suicides can be seen as essentially homicidal, with the killer subsequently dying by suicide, perhaps out of remorse. Alternatively, it can be seen as a suicide extended to intimate relations
Our study has several limitations. Firstly, it relied on decennial census information for information about eligible households and their composition. The analysis thus excluded events that involved individuals not sharing the same household at the time of one of the two censuses, or events concerning individuals never registered as living together. Interestingly, the homicide-suicide offending rates observed in current study (0.09 and 0.10 per 100,000 in 1991 and 2001, respectively) are closely similar to the rate from a study of cases where an autopsy had been performed (0.09 per 100,000 for the period 1992–2004)
In conclusion, this national longitudinal study in a country with wide-spread access to firearms shows that living conditions associated with psychological stress and lower levels of social support are associated with homicide-suicide events. Conversely, the study found no evidence that homicide-suicide was associated with education or occupation, nationality or the presence of children in the household. The linkage of criminological, forensic and psychological data with the national cohort study will overcome some of the limitations of the present study and allow more detailed characterisation of events, including the role of military and other firearms. Almost all incidents involved firearms and results thus add to a growing body of evidence that in Switzerland and elsewhere restricting access to firearms might prevent at least some homicide-suicide tragedies.
The authors thank the Federal Statistical Office whose support made the Swiss National Cohort and this study possible.