A comparison of older and younger offenders with delusional jealousy

Abstract

We sought to determine whether or not there were differences in medical, criminological and legal factors between older and younger offenders with diagnoses of delusional jealousy by undertaking a retrospective case-file search of Australian legal databases. Our results demonstrate that older offenders were more likely to have comorbid dementia whereas younger offenders were more likely to have comorbid substance use and chronic psychotic conditions. A history of domestic violence frequently predated the index offence but we were unable to determine if this was due to psychosis or a pre-existing tendency for violence. Despite a common diagnosis, the older offenders were more likely to be made forensic patients rather than sentenced prisoners when compared with the younger offenders. Consequently, different factors might mediate the pathway to violence in older and younger people suffering from delusional jealousy and could be additional targets for clinical intervention.

Introduction

Delusions are ‘fixed beliefs that are not amenable to change despite conflicting evidence’ (American Psychiatric Association, 2013:87). Delusional (or morbid) jealousy, also known as Othello syndrome, is a content-specific form of non-bizarre psychosis wherein a person believes with delusional intensity that somebody else – usually an intimate partner – has been unfaithful (Batinic et al., 2013). The delusion is a paranoid one and is symptomatic of a number of neuropsychiatric diseases, including psychotic conditions such as delusional disorder and schizophrenia (Soyka et al., 1991), neurological conditions such as dementia (Cipriani et al., 2012; Soyka, 1992; Tsai et al., 1997) and mood disorders (Soyka et al., 1991; Soyka & Schmidt, 2011).

As the general population ages and the proportion of older people in the community increases, healthcare services are increasingly accommodating those with chronic and degenerative conditions, including those that affect the brain (Denton & Spencer, 2010). The criminal justice system is similarly seeing the effects of population ageing, with increasing numbers of older offenders and an increasing proportion of elderly people being housed in correctional facilities (Baidawi et al., 2011; Stavrou, 2017; Trotter & Baidawi, 2015).

In Australia, the number of people aged over 65 who are in prison has increased by 348% since 2012, with healthcare and special housing requirements projected to increase by as much as 70 to 90% in the next decade (Ginnivan et al., 2018). Although the literature focuses on the health needs of older prisoners (Fazel, Hope, O’Donnell, & Jacoby, 2001; Fazel, Hope, O’Donnell, Piper, & Jacoby, 2001; Hayes et al., 2012), greater research into the comorbid conditions and risk factors that uniquely contribute to offending in older people is required. It is important to identify risk factors for criminal offending related to comorbid neurological conditions such as dementia while also remaining cognisant of the possibility for unique interactions between an individual’s long-term (criminogenic) risk factors for criminal offending and a potential ‘unmasking’ or heightening effect triggered by the onset of degenerative neurological conditions. Identifying characteristics of offending in older people is important for several reasons, including an increased appreciation for the need to evaluate cognitive function in older offenders and the development of age-appropriate risk assessment tools. Greater awareness of comorbid factors that influence or contribute to offending by older people increases the likelihood of appropriate justice system responses and judicial decisions that consider these factors, as well as the possibility of diversion programmes for older offenders.

Delusional jealousy occurs in a number of psychiatric and neurological conditions. Soyka et al. (1991) reported a 1.1% prevalence of delusional jealousy in 8134 psychiatric patients. In a subsequent replication of their original study, Soyka and Schmidt (2011) found 72 cases of delusional jealousy in 14,309 patients admitted to a psychiatric hospital over an 8-year period, a lower prevalence of 0.5%. Of these cases, about 60% had a psychotic condition (characterised as schizophrenia, delusional disorder or schizotypal). Interestingly, among the patients diagnosed with delusional disorder, most had delusional jealousy (78.3%). Mood disorders were diagnosed in almost 20% of cases (14 out of 72), whereas organic mental disorders and substance use disorders were diagnosed in about 7% of cases (n = 5; Soyka & Schmidt, 2011).

The manifestation of delusional jealousy in people with neurological conditions could help to identify the brain circuits underlying the pathophysiology of this condition. Tsai et al. (1997) examined 133 inpatients with dementia and found that 21 were suffering from delusional jealousy (15.8%), with roughly equal numbers having Alzheimer’s dementia (16%), multi-infarct dementia (15%) and unspecified dementia (16.7%). Hashimoto et al. (2015) found that 8.7% of 208 patients with dementia had delusional jealousy, of whom almost one quarter had Lewy Body Dementia (23.6%), whereas cases associated with Alzheimer’s disease (5.5%) and vascular dementias (4.8%) were less common. Of interest, most of the inpatients (10 out of 18) were at the mild stages of dementia and 11 had demonstrated violence (Hashimoto et al., 2015).

Other neurological conditions are also common in those diagnosed with delusional jealousy. A retrospective case series that scrutinised the medical records of patients with delusional jealousy found that the condition was more likely to be associated with a neurological condition than with a psychiatric disorder (69.5% versus 30.5%; Graff-Radford et al., 2012). Of the 73 neurological conditions, 5 were due to brain lesions and the remainder to dementias of various aetiologies, with Lewy Body Dementia the most common subtype. This study also revealed that the average age of onset was 68 years (although the spread of ages ranged from 25 to 94 years) and that most diagnosed cases were in men (61.9%; Graff-Radford et al., 2012).

Case reports suggest that pathology in the right hemisphere of the brain is involved, with delusions of infidelity documented after right middle cerebral artery stroke (Luaute et al., 2008; Ortigue & Bianchi-Demicheli, 2011), right thalamic infarction (Soyka, 1998) and right orbitofrontal meningioma (Narumoto et al., 2006). In Graff-Radford et al.’s (2012) study, 14 patients underwent volumetric magnetic resonance imaging (MRI) and were matched with patients of the same age, diagnosis and gender as well as with a group of healthy controls. Those with delusions of infidelity had ‘greater grey matter loss predominantly in the dorsolateral frontal lobes, particularly in superior frontal gyri, and right posterior lateral temporal lobe…’ (Graff-Radford et al., 2012:41). This suggestion of a right hemispheric basis of delusional jealousy is consistent with evidence and theories indicating that the right hemisphere might be important for the production of delusional thought (Gurin & Blum, 2017).

Interestingly, there are a number of reports documenting the development of delusional jealousy among those treated for Parkinson’s disease with dopaminergic medication (Georgiev et al., 2010; Graff-Radford et al., 2010, 2012; Perugi et al., 2013). Cessation or reduction of dopaminergic medication can lead to the resolution of the psychotic symptoms, suggesting that dopaminergic dysregulation is involved (Georgiev et al., 2010; Kataoka & Sugie, 2018; Perugi et al., 2013).

Among the range of symptoms of psychosis, the presence of delusional jealousy is of particular concern because of its link with violence and aggression (Kingham & Gordon, 2004; Leong et al., 1994; Silva et al., 1998; Soyka & Schmidt, 2011), particularly against spouses (Silva et al., 1998). This remains a risk even in older age. A retrospective study of 70 older homicide offenders (aged over 55 years) found that 6 of the 13 offenders who were diagnosed with psychosis had delusional jealousy (Reutens et al., 2015). If this psychiatric condition is a particular risk factor for violence in the elderly, a population that does not usually display violence, it would be of clinical utility and benefit to the justice system to determine the factors associated with this condition that might mitigate culpability or serve as a warning signal of impending violence.

To date, no published studies have examined the legal outcomes of people who commit serious crimes related to delusional jealousy. In Australia, the Mental Health Act of each state and territory acknowledges the needs and legal rights of people with mental health conditions, including those who are accused of committing a crime (Parliament of Australia, 2006). If a person’s mental illness or impairment impacts on their right to a fair trial or is determined to have contributed to the offending, there are a range of options for diversion, care, treatment, control and mitigation (Davidson et al., 2017).

In this study we examine the links between neuropsychiatric conditions and delusional jealousy in people who were charged with committing a serious violent crime in Australia over the period covered by online court databases. We examine whether or not there are factors that differ according to the age of the offender and how the legal system incorporated the medical information into the delivery of justice outcomes. Furthermore, we seek to determine whether or not there are differences in the legal outcomes of people who have committed crimes related to delusions of infidelity depending on their age.

Materials and methods

The lead author (SR) examined case law from Australian states and territories using two online legal databases. The Australasian Legal Information Institute (AustLII) is an open access legal resource run by the University of Technology (UTS) and University of New South Wales (UNSW) faculties of law that includes case law databases from New Zealand, all Australian territories and states and the Commonwealth of Australia (http://www.austlii.edu.au). The breadth of the included cases differs according to state and jurisdiction: the New South Wales (NSW) Supreme Court data set contains cases from June 1993 onwards; the Western Australian Supreme Court data set contains cases from 1964 onwards; the Victorian and Queensland Supreme Court data sets start from 1994; the Tasmanian Supreme Court data set starts from 1985; the South Australian Supreme Court data set starts from 1989; and the Australian Capital Territory and Northern Territory Supreme Court data sets contain cases from 1986 onwards. The second database we used, WestLawAu, is an international legal subscription service provided by Thomson Reuters (https://www.westlaw.com.au).

Firstly, the two databases were searched using the following search terms:

Delusions & jealousy, Delusions & infidelity, Othello Syndrome, Delusional Jealousy, psychosis and jealousy, psychosis and infidelity.

Cases were limited to serious indictable offenses whereby a person had the right to have the matter heard before a judge and jury. All states and territories in Australia recognise the role that mental illness can play in the commission of offenses, and recognise that an accused person may not have the capacity to participate in their own trial or that mental illness might have robbed them of their capacity to know what they were doing at the time of the offence or to understand that it was wrong (Parliament of Australia, 2006). Offenders aged 50 years and over were placed in the older group and those aged under 50 years were placed in the younger group. The designation of people aged 50 years and over as older is based on the Australian Institute of Criminology’s 2011 report which notes that this is a commonly used definition of an older prisoner (Baidawi et al., 2011). This age is used in other Australian government publications including a 2010 Victorian Department of Justice report collating research on older prisoners (Turner & Trotter, 2010) and a NSW parliamentary research service report on older prisoners (Angus, 2015). Demographic data of the offenders, their victims and their crimes were extracted from the reports and tabulated for comparison.

Results

The search identified 28 younger and 13 older offenders from the two legal databases whose crimes had occurred between 1987 and 2017.

Demographic data – younger group

A total of 27 offenders were aged under 50 years (younger group) of which 26 were men. Data on age at the time of the offence were obtainable for 24 offenders and ranged from 28 to 48 years (median = 36.5 years).

All charges included violence, with 18 initial charges of murder (1 offender had 2 counts applied). Other charges involved assault (n = 2), attempted murder (n = 2), deprivation of liberty (n = 1) and grievous bodily harm (n = 3).

Of the 29 victims, 6 were male (20.7%) and the remainder were female. A total of 24 victims were a current or former partner of the offender (82.8%), and the other 5 victims were all known to the offender: a friend, an uncle of a victim, a brother-in-law, a distant relative of an offender’s wife and a case worker (all ns = 1). The details of the younger group are given in Table 2.

Table 2.

Younger group.

Age (years), Sex	Victim(s) Relation to Offender	Relation Duration (years)	Suspected Affair Partners	Victim(s) Age (years), Sex*	Method of Assault	Drug Use	Charge	Sentence	Comorbid Conditions	PCC	PDVO
32, M	Partner/ fiancée	3	Multiple males and females	21, F	Kicks/blows	No evidence	Murder	Life	Delusions of infidelity, Multiple sclerosis	–	Yes
–, M	Partner	–	–	–,–	Strangle	Alcohol	Murder	NGMI	Delusional disorder, Major depression	–	Yes
30, M	Partner	10	Unknown	29, F	Kicks/blows	Amph.	Murder	21 years	Amphetamine use disorder, Paranoid psychosis	Violence, burglary	Yes
37, M	Wife	6	Multiple males	26, F	Blunt inst.	No	Assault occ. bodily harm while armed, Assault occ. bodily harm, Dep liberty, Breach DVO	Unfit/ forensic	Delusional jealousy	DVO 12 days previously	Yes
42, M	Wife	–	Unknown males	–, F	Blunt inst., Strangle	No alcohol at time	Attempted murder, Dep liberty, Acts intended to cause GBH	NGMI	Schizophrenia, Alcohol abuse	Fighting in youth	Yes
31, F	Husband	10	Neighbour, ‘Tracey’	–, M	Knife	Not intoxicated	Breach DVO, GBH	NGMI	Schizoaffective, Substance use disorders	No	Yes
28, M	Partner	0.4	5 men, 1 woman, friends, brother	30, F	Knife	Methamph.	Murder	Life	Paranoid schizophrenia, Substance use disorders	Assault, Property damage	Yes
43, M	Wife	7	Unknown	–, F	Tied up and gagged	Alcohol	Detain with intent to obtain advantage	4 years	Major depression with psychotic features, Alcohol use disorder	–	Yes
40, M	Partner	6	Unknown	–, F	Knife, Strangle	No	Murder reduced to manslaughter	9 years	Cannabis use disorder, Delusional disorder	Minor Property offenses	Yes
35, M	Ex-wife	>15	Ex-wife’s manager	31, F; 37, M	Knife	No	Murder	NGMI	Schizophrenia or Delusional disorder	–	Yes
37, M	Wife	12	His friends	34, F	Knife	Amph., Cannabis	Murder	Life	Schizophrenia, Substance use disorder	–	Yes
36, M	Partner (F) and friend (M)	>10	Unknown	31, F; 37, M	Strangle, Knife, Blunt inst.	Meth, Prescription drugs, Steroids	Murder x 2	Life	Major depression, Delusional jealousy, Substance use disorder	No	No
–, M	Wife	–	‘Other men’	–, F	Knife, Blunt inst., Strangle	No	GBH	5 years	Schizophrenia/ Schizoaffective disorder	No evidence	No evidence
48, M	Wife	8	Wife’s teenage son’s friends	45, F	Blunt inst., Knife	Alprazolam	Murder	NGMI	Schizophrenia	No evidence	Yes
35, M	Partner	–	Multiple males	–, F	Strangle	Amph., Opiates	Murder reduced to manslaughter	–	Schizophrenia, Substance use disorder	–	No evidence
48, M	Wife	13	Neighbour	38, F	Gun	No	Murder	15 years	Delusional disorder	No	Yes
41, M	Wife	23	Multiple men	40, F	Knife	No	Murder	NGMI	Schizophrenia	DVO 2 months before	Yes
36, M	Wife	18	Unknown harassers	35, F	Blunt inst., Kicks/blows	No	Murder reduced to manslaughter	10 years	Delusional disorder	Multiple	Yes
28, M	Case worker	–	Believed he was kidnapping girlfriend	48, M	Kicks/blows, Knife	No	Murder	NGMI	Schizoaffective disorder, Substance use disorder	–	No evidence
39, M	Ex-wife and her uncle	12 (ex), married 7	Ex-wife’s uncle	39, M	Gun	No	Murder, Intent to murder, Damage by fire, et al.	NGMI	Delusional disorder	No	No
29, M	Partner	8	Unknown man, says victim admitted it	25, F	Knife	Alcohol, Cannabis	Murder	Life	Delusional disorder	Extensive	Yes
40, M	Acquaintance	Not seen for 6 or 7 years	Acquaintance with wife, daughter and sister	54, M	Run over with car, Blunt inst.	No	Murder	Unfit, NGMI	Schizophrenia	Yes	No
30, M	Brother-in-law	–	Victim	–, M	Kicks/blows	Cannabis	Intentionally cause serious injury	6 years	Drug-induced psychosis	CCO for assault against wife	Yes
42, M	Girlfriend	–	Affair with former husband	–, F	Sexual assault × 2	No	Sexual assault × 2, Actual bodily harm	NGMI	Schizophrenia	No evidence	No evidence
–, M	Girlfriend	–	–	–, F	Sexual assault, Blunt inst., Kicks/blows	Unknown	Reckless cause GBH, Malicious damage, Sexual intercourse × 2	12 years	Schizophrenia, Substance use disorders	Alcohol	Yes
–, –	Wife	–	–	Mid 40s, F	Blunt inst., Set on fire	No	Attempted murder	Sentence unknown	Alcohol use disorder, Epilepsy, Delusions of infidelity	AVO just before	Yes

Note. Amph = amphetamines; AVO = apprehended violence order; CCO = community corrections order; DVO = domestic violence order; GBH = grievous bodily harm; Methamph = methamphetamines; NGMI = not guilty by reason of mental illness; PCC = previous criminal charge; PDVO = previous domestic violence offence.

Demographic data – older group

A total of 13 offenders were aged over 50 years (older group), all of whom were men. The mean age of the offenders was 63.7 years (median = 58 years; range = 52–87). The majority were charged with homicide (n = 10), and there were charges of stalking and arson (n = 1) and assault (n = 2). A total of 12 of the victims were women and 2 were men (one person killed 2 people). All of the women had been or were in an intimate relationship with the offender. The details of the older group are given in Table 3.

Table 3.

Older group.

Age (years), Sex	Victim(s) Relation to Offender	Suspected Affair Partner(s)	Victim(s) Age (years), Sex	Method of Assault	Drug Use	Charge	Sentence	Comorbid Conditions	PCC	PDVO
52, M	Son-in-law	Son-in-law	36, M	Gun	Alcohol, Cannabis	Murder	23 years	Delusional disorder, Severe dyslexia	Yes	Yes
87, M	Wife	Neighbour	86, F	Knife	No	Murder	NGMI	Vascular dementia, Previous suicidal ideation	No	Yes
55, M	Wife	Various	46, F	Blunt inst.	No	Murder	NGMI	Delusional disorder	Yes	Yes
66, M	Wife	Various	39, F	Knife	No	Murder	NGMI	Paranoid schizophrenia	No	Yes
58, M	Partner	Various	–, F	Blunt inst.	No	Murder	NGMI	Delusional disorder		Yes
78, M	Partner	Drug lord (named)	70, F	Strangle	No	Murder reduced to manslaughter	7.5 years	Mild dementia, Delusional jealousy	No	Yes
56, M	Wife	Various	59, F; 17, F	Strangle, Blunt inst., Knife,	No	Attempted unlawful killing, Unlawful wounding	NGMI, Unfit	Lewy Body Dementia	No	No
68, M	Co-resident (ACF)	–	87, M	Kicks/blows	No	Intent to cause serious injury	Treatment order	Paranoid personality, Frontotemporal impairment secondary to stroke and head injury, Hx of addiction to painkillers, Depression	Yes	Yes
77, M	Wife	Wife’s GP	74, F	Knife	No	Murder	NGMI	Vascular and Alzheimer’s dementia, Depression	No	No
55, M	Wife	Various	53, F	Knife Blunt inst.	No	Murder	NGMI	Major depression, Delusional disorder	No	No
62, M	Wife	Various	47, F	Blunt inst.	No	Murder	6 years 3 months	Vascular dementia, Delusional disorder, Major depression	No	–
57, M	Wife	Various	54, F; 27, M	Knife	No	Murder, Wound with intent	28 years	Delusional disorder	No	Yes
57, M	Ex-partner	Resident of caravan park	–, F	Fire	No	Arson, stalking	NGMI, Unfit	Bipolar disorder	Yes	Yes

Note. Hx = History; NGMI = not guilty by reason of mental illness; PCC = previous criminal charge; PDVO = previous domestic violence offence.

Criminological factors

Some offenders used multiple methods to kill or injure their victim and all methods are included in this analysis (see Table 1). Stabbing was found to be the most common method in both the older (n = 6, 37.5%) and younger (n = 11, 28.2%) groups. Blows and kicks or strangulation were the next most common method for the younger group (n = 6, 15.4%) whereas the use of a blunt instrument was the next most common method in the older group (n = 5, 31.3%), with strangulation attempts occurring in only 2 cases (12.5%). Kicks and blows occurred in only 1 case in the older group (6.3%). Firearms were used in 2 cases in the younger group (5.1%) and in 1 case in the older group (6.3%).

Table 1.

Method of injury used by younger (n = 39) and older (n = 16) offenders.

	Younger, n (%)	Older, n (%)
Blows and/or kicks	6 (15.4%)	1 (6.3%)
Blunt instrument	9 (23.1%)	5 (31.3%)
Stabbing	11 (28.2%)	6 (37.5%)
Strangulation/attempted strangulation	6 (15.4%)	2 (12.5%)
Shooting	2 (5.1%)	1 (6.3%)
Sexual assault	2 (5.1%)	0 (0.0%)
Other	3 (7.7%)	1 (6.3%)
TOTAL	39 (100.0%)	16 (100.0%)

A history of physical or verbal violence or controlling behaviour preceding the criminal incident was noted in most of the young offenders (19 out of 27, 70.4%), with no mention recorded in the rest of the group. Over two thirds of the older group had a history of verbal or physical violence prior to the events for which they were charged (9 out of 13, 69.2%), 3 offenders did not have a history of violence leading up to the crime (23.1%) and 1 offender did not have such a history mentioned (7.7%).

Medical and psychiatric factors

Delusional disorder was diagnosed with about equal frequency in the younger and older groups – in 9 offenders in the younger group (33.3%) and 5 offenders in the older group (38.5%). Schizophrenia or schizoaffective disorder was the most commonly diagnosed condition in the younger group (n = 12, 44.4%) and 1 offender had a diagnosis of either schizophrenia or delusional disorder. In the older group, 1 offender was diagnosed with either schizophrenia or delusional disorder but there were no other diagnoses of schizophrenia.

Dementia was the most commonly diagnosed condition in the older group (n = 5, 38.5%). Of those with dementia, 2 offenders were diagnosed with vascular dementia, 1 with Lewy Body Dementia and 1 with mixed vascular and Alzheimer’s dementia. Additionally, 1 older offender had a diagnosis of comorbid major depression, frontotemporal impairment and delusional disorder. Thus, almost half of this group (46.2%) had an underlying neurological condition. If limiting the older group to the 6 offenders aged over 60, the prevalence of a neurological condition increases to 83.3%, with two thirds having had a dementia diagnosis (n = 4). Only 2 offenders in the younger group had a comorbid neurological condition (5.1%) – 1 offender with a diagnosis of epilepsy and the other with a diagnosis of multiple sclerosis – and there were no diagnoses of dementia.

In the younger group, 12 offenders had a substance use disorder, of whom 3 had an alcohol use disorder (25%). The case records note that 10 of the younger offenders had taken substances prior to the offence, including alcohol, illicit drugs and prescription medications. Only 1 offender in the older group was intoxicated at the time of his offending (7.69%), and none had a current diagnosis of substance use disorder.

Legal outcome

Almost half of the younger group were made forensic patients by the court (n = 11, 40.7%), with 2 offenders found unfit to stand trial, 1 placed on a community treatment order (a legal order made under the Mental Health Act of a state mandating that the offender accept treatment while living in the community) and the rest found not guilty due to mental illness (including 1 offender who was found both unfit to stand trial and not guilty due to mental illness). A further 3 offenders in the younger group (12.5%) had their charges reduced to manslaughter from murder due to a partial defence of mental illness, and the rest did not receive a reduction in charges (n = 11, 40.7%).

More than two thirds of the older group were given a forensic order (n = 9, 69.2%), with 1 offender given a community corrections order. A further 2 offenders had their charges reduced from murder to manslaughter and only 2 offenders were sentenced for the original charges (15.4%), which were murder for 1 offender and murder and wound with intent for the other.

Discussion

This study has identified 40 cases of delusional jealousy processed in Australian courts between 1987 and 2017. Although this is a relatively low rate of cases, the findings provide evidence for an association between delusional jealousy and violent offences, including assault and murder. Approximately two thirds of the identified delusional jealousy cases occurred in those under 50 years of age. A history of abusive behaviour towards an intimate partner preceding the offence is apparent in over two thirds of the cases involving younger offenders (19 out of 27, 70.4%) and in a similar proportion of the cases involving older offenders (9 out of 13, 69.2%), but there are insufficient data to determine whether or not the behaviours were delusionally driven. Abusive behaviours in the context of delusional beliefs of infidelity or a history of domestic violence should serve as a warning sign for intervention and need to be specifically excluded on clinical assessment.

Consistent with the nature of the delusion, a current or past intimate partner is at most risk of violence, likely because of their perceived betrayal of the delusional individual (n = 29, 83.3% of the victims), but the suspected affair partners were also targeted by some offenders (n = 5, 11.9%). Whereas some of the offenders gave general or non-specific opinions as to the nature and identity of the affair partner such as ‘neighbours’ or ‘other men’, others were convinced as to the identity of the affair partner and their accounts suggested that they sought revenge on them.

As expected, a notable proportion of the offenders aged 50 years and over qualified for a diagnosis of dementia (n = 5, 38.5%) whereas those younger than 50 years were more likely to have a primary psychotic disorder with comorbid substance abuse, suggesting that different factors might mediate the pathway to violence in these two groups. In people with dementia, the commission of severe violence might be related to neurodegenerative changes that are associated with aggression, impaired judgement and impulse control (Cipriani et al., 2016). In the case of the younger offenders, the association between substance use, psychosis and violence is consistent with the literature (Butler et al., 2011; Swanson et al., 1996). Additionally, the association between delusional jealousy and aggression is consistent with other findings (Cipriani et al., 2012; Silva et al., 1998; Soyka & Schmidt, 2011). However, unlike Soyka and Schmidt (2011), who reported a low prevalence of substance abuse in their sample of psychiatric inpatients with delusional jealousy (0.1%), our findings indicate that one third of the younger offenders and one quarter of all offenders had a comorbid substance use disorder. This difference might be caused by our sample being drawn from a database of offenders who have demonstrated significant violence – and this suggests that substance abuse could be a key factor mediating violent behaviour in younger people with delusional jealousy, acting as a tipping point in this scenario.

All offenders diagnosed with dementia had undergone neuroimaging, clinical assessment and cognitive testing. A range of clinical disciplines were involved in the diagnoses. A neuropsychiatrist or psychogeriatrician diagnosed three of the offenders with dementia, the fourth was diagnosed by a team comprising a neurologist, a neuropsychiatrist and a neuropsychologist, the fifth diagnosis was made by a forensic psychiatrist and a clinical psychologist based on a battery of psychometric tests and in the sixth case several psychiatrists reported frontotemporal impairment secondary to stroke and head injury. It can be assumed that the dementia was not severe in most cases, as all but one of these offenders were found to be capable of participating in their trials. The numbers are small, but most of the offenders identified as having dementia had a diagnosis of vascular dementia (4 out of 6), either as the main diagnosis or comorbid with Alzheimer’s disease or, in one case, head injury. This differs from the findings of Hashimoto et al. (2015), who found that Lewy Body Dementia was the most common diagnosis in their group of 18 people with dementia-related delusional jealousy (n = 10, 55.5%), compared with vascular dementia (n = 1, 5.6%) and Alzheimer’s dementia (n = 7, 38.9%).

Stabbing was found to be the most frequent method of offending for both groups; it was involved in 28.2% of the cases in the younger group and 37.5% of the cases in the older group, consistent with another study of homicide in Australia (Soyka et al., 1991). This method is closely followed by the use of a blunt instrument. Together, these methods account for approximately half of the cases in the younger group and nearly two thirds of the cases in the older group.

Despite sharing the common diagnosis of a psychotic delusion of infidelity, the group of offenders aged 50 years and over had different legal outcomes to those aged under 50 years. Over two thirds of the older group (69.2%) were judged to have a degree of impaired capacity that rendered them either not guilty due to mental illness (NGMI), unable to stand trial or deserving of reduced charges (e.g. from murder to manslaughter). In contrast, just less than half of the younger group (48.1%) did not see an alteration in their charges.

In Australia, the legal tests for unfitness and mental impairment are derived from the same precedents, but the criteria vary between jurisdictions. While it is understandable that a person with cognitive impairment might not be able to fulfil the tenets of the Presser Criteria from R v. Presser [1958] VR 45, which involve a person’s ability to understand and plead to a charge, understand the nature of the proceedings, provide a defence and instruct their legal representative, the finding of NGMI is derived from a different set of criteria – the M’Naughten rules (arising from M’Naughten’s Case [1843] 4 St Tr [NS] 847; 8 ER 718). To establish a defence of mental illness, the accused must either be labouring under a defect of reason caused by a disease of the mind as a result of which they did not know the nature and quality of their act, or if they did know the nature and quality of the act, they did not know that it was wrong (Howard & Westmore, 2010). Given that the offenders in both the younger and older groups could be said to have been suffering from similar defects of reason resulting from a delusion caused by mental illness (a disease of the mind), further exploration is required to determine what other factors led to the differing legal decisions. It is unlikely to have been due to significant cognitive impairment, as all but 2 of the 13 older offenders were deemed capable of standing trial – and of the 2 who were considered not capable, 1 offender had a diagnosis of bipolar disorder rather than a cognitive impairment.

Decisions on culpability in mental illness are complex, involving a nexus between the law and expert medical opinion. Whereas severity of mental illness and cognitive impairment occur on a continuum, legal decisions tend to be binary – guilty versus not guilty, fit for trial versus not fit or a finding that the offence was (or was not) committed due to mental illness. Given these binary constraints, how is a decision made as to where the demarcation lies? The medical experts who provide their opinions are required to grapple with this concept – but the ultimate decision is a legal one, and expert evidence does not have to be accepted by the judge or jury. Further research is required to elucidate the weighting that is placed on aspects of medical evidence.

Limitations

This study examines cases reported within a comprehensive case law database. However, the database only includes published case law and so is not an exhaustive database of all legal cases of delusional jealousy in Australia. As this is a case law study, the medical data that could be extracted are limited to those required by the court. However, as the offenders’ psychiatric conditions were central to their cases, all of them had undergone a psychiatric assessment and diagnosis, a fairly detailed summary of which is contained in the published findings.

Conclusion

The results of this study indicate that most people who have been violent in relation to jealous delusions have a history of violence towards an intimate partner. Where a patient presents to medical services with symptoms fitting delusional jealousy, this behoves clinicians to obtain a history of violence both from the patient and, if permitted, from the family. This history should be used to firstly ascertain whether or not the patient has ever acted on their delusional beliefs, secondly seek to understand their general propensity for violence and thirdly educate the patient’s family regarding the known risk of violence associated with delusional jealousy. If a specific person is named as the suspected affair partner, further exploration is required to ascertain the degree of risk of harm to that person.

This study suggests that there are differences in the clinical diagnoses and legal outcomes of older and younger people who have committed violent acts as a result of delusions of infidelity, with the caveat that the numbers are small and suppression orders in some jurisdictions might prevent the publication of cases related to mental impairment or unfitness. Substance abuse might be a mediating factor for violence in younger people whereas dementia was found to be a comorbid feature in a significant number of older people, who were more likely to be found NGMI. Neurological conditions were found to be common in those aged over 60 years, confirming the results of other studies that have also found a neurological association with the development of this type of delusion. From a clinical perspective, it is recommended that people aged over 60 years who present with delusions of infidelity are examined for neurological conditions and that their risk for violence is ascertained.

Additionally, further research into the reasons for the disparate legal outcomes between younger and older offenders with this shared behaviour is required in order to determine how professionals in the legal system weigh the medical and psychiatric evidence before them, as well as how the decision-making processes involved in deciding culpability are undertaken.

Ethical standards

Declaration of conflicts of interest

Sharon Reutens has declared no conflicts of interest.

Tony Butler has declared no conflicts of interest.

Ye In Jane Hwang has declared no conflicts of interest.

Adrienne Withall has declared no conflicts of interest.

Ethical approval

This article does not contain any studies with human participants or animals performed by any of the authors.