An examination of criminal offenders with dementia in Australian courts

Abstract

This study aims to characterize people with dementia who were charged with criminal offences between 1995 and 2020 and describe their offending. Court cases were derived from Australian legal databases and descriptive data were manually extracted from case reports. Of 62 people variously charged with homicide, assault, child sexual assault, breach of conditions, property and larceny offences, driving offences, perverting the course of justice and arson, 46 were identified as having executive dysfunction, either as stated by medical expert witnesses or implicitly, due to conditions like Huntington’s disease and frontotemporal dementia. Offending history was found to differ depending on offence type and dementia type. Executive dysfunction appears to underly offending in the sample; furthermore, some disease factors may combine to ‘inhibit’ or ‘permit’ offending. Permitting factors include executive dysfunction and younger age at time of offending; inhibitory factors include dementia-related impacts on mobility, memory and reaction speed.

Keywords:

• older offender
• older criminal
• dementia
• crime
• homicide
• offending

Introduction

Over the past 20 years, attention has been drawn to the growth in the number of older people in the justice system (Stewart & Schollum, 2021) and the increased psychological and physical comorbidities that older inmates experience in comparison to similar aged peers in the community and their younger prison counterparts (Fazel et al., 2001; Kingston et al., 2011). Reasons for the increase in older offender numbers are likely to be multifaceted, reflecting general trends such as the ageing population (Angus, 2015; Potter et al., 2007) and longer sentencing for serious crimes (Huntley et al., 2019) as well as specific factors such as technological advances that allow the detection of historic crimes and changed community attitudes towards child sexual abuse which have led to reforms in the prosecution and sentencing of historical abuse matters (Shead, 2014).

Research into late-in-life criminal offending is important for several reasons. First, many countries are experiencing population ageing and longer life spans, so prisons will increasingly need to accommodate older prisoners and prisoners with age-related cognitive decline, leading to increased resource utilization as many older prisoners have comorbid ill-health (Baidawi et al., 2011; Fazel et al., 2002). Second, interventions to avert or modify offending behaviors can be developed if risk factors are identified. Third, diversion pathways can be considered for those whose responsibility for their criminal actions is diminished but who still require containment and discipline. Finally, risk assessment models are heavily geared towards early life criminogenic factors and would be enhanced by determining factors that are associated with repeat offending and are specific to older people with offending behavior.

The putative role of brain abnormalities in offending behaviors requires the amalgamation of pathological, criminological and clinical research. Studying people with neurodegenerative conditions such as dementia who offend for the first time later in their lives may offer insights into the neurological basis of criminal offending across the age span. This may affect the notion of criminal responsibility and give rise to potential treatment strategies. Such research has mainly focused on frontotemporal dementias – a group of dementias that affect the frontal and anterior temporal lobes of the brain. People with frontotemporal dementia usually present in their forties and fifties with an array of symptoms depending on the subtype and location of the brain pathology. For instance, some subtypes present with profound language and speech impairments (Bang et al., 2015) whereas another subtype, behavioral variant frontotemporal dementia, predominantly presents with impairments of executive functioning manifesting as impulsivity, socially inappropriate behavior (Bang et al., 2015) and lack of empathy (Darby et al., 2016; Mendez, 2022). People with executive dysfunction also have difficulties processing rewards and punishments (Darby et al., 2016), which affects their judgment and can predispose them to offending behaviors. Due to their relatively young age and a lack of more typical cognitive deficits associated with dementia, such as memory impairment, the diagnosis of people with frontotemporal dementia can be missed or considerably delayed (van Vliet et al., 2013).

Research into the criminal offending of people with behavioral variant frontotemporal dementia has noted that its characteristic socially inappropriate behavior can result in the commission of offences including assault, stealing and driving offences (Miller et al., 1997). More serious offences including sexual crimes (Mendez & Shapira, 2011) and murder have also been reported (Mendez, 2022), with the offending occurring in a reactive rather than planned manner. Several studies have found increased offending in people with frontotemporal dementia compared to other dementias (Liljegren et al., 2015, 2019; Talaslahti et al., 2021). For example, a retrospective case review of 2397 people with dementia reported on criminal-type behaviors gleaned from medical records. Patients with semantic variant primary progressive aphasia – a language subtype of frontotemporal dementia – and behavioral variant frontotemporal dementia were found to be more likely to exhibit such behaviors, whereas those with Alzheimer’s dementia were least likely (Liljegren et al., 2015). Another study examined 101 cases of people with Alzheimer’s dementia and 119 cases with frontotemporal dementia who had neuropathological confirmation of their diagnoses and reviewed their medical files for evidence of criminal-type behaviors. These behaviors were more prevalent in the frontotemporal dementia group across all categories, with the exception of public urination (Liljegren et al., 2019). Furthermore, a study of linked dementia diagnoses and criminal records found that criminal offending preceded the diagnosis in both frontotemporal dementia and Alzheimer’s dementia and found that serious crimes such as murder and attempted murder were rare – only two such cases were found out of the 92,191 patients studied, and both were committed by people with frontotemporal dementia (Talaslahti et al., 2021). Two studies also noted that offending may precede the clinical diagnosis of frontotemporal dementia (Talaslahti et al., 2021) or be the first indication of the condition (Liljegren et al., 2015).

Of the other dementias, Huntington’s disease has been shown to be associated with relatively high rates of criminal offending (Jensen et al., 1998; Liljegren et al., 2015). One post-mortem study of 204 people who had ‘behaviors that could be included as criminal’ found that 20% of the 30 people with Huntington’s disease had demonstrated criminal-type behaviors (Liljegren et al., 2015). The behaviors are at the lower end of the severity scale, however, such as traffic violations. Of note, another study using court conviction data found that, compared to controls drawn from community registers and first-degree relatives, increased rates of offending were only evident in men (Jensen et al., 1998).

Alcohol-related dementias are another diagnostic category present in the majority of studies examining criminal offending in older, cognitively impaired individuals, whereas Alzheimer’s dementia has been identified less frequently than other dementias (Barak et al., 1995; Ekström et al., 2017; Heinik et al., 1994; Kim et al., 2011). Wang et al. (2018) however did not find an association between subtype of dementia and crime in their study of 47 offenders. This might be the result of their sample size or because the dementia types were classified as senile, traumatic organic, non-traumatic organic, vascular and unknown rather than diagnoses such as Alzheimer’s dementia, dementia with Lewy bodies and frontotemporal dementias.

Overall, the small case numbers within existing research studies have limited the ability to draw inferences on a putative link between dementia subtype and crime (Barak et al., 1995; Curtice et al., 2003; Ekström et al., 2017; Heinik et al., 1994; Kim et al., 2011), with the largest study examining the case records of 47 offenders (Wang et al., 2018). Liljegren et al. (2019) reported a thorough study of neuropathologically diagnosed Alzheimer’s dementia and frontotemporal dementia in people who displayed behaviors that the authors considered amounted to criminal behavior, but these behaviors were not tested by the police or justice system and did not include violent behaviors.

In this study we seek to characterize people with dementia who have been charged with a criminal offence using a caselaw sample derived from Australian legal databases, with the aim of describing offending or type of offending in people with cognitive impairment. The identification of such factors would assist clinicians with assessing the potential for future offending.

Method

A search for cases where the offender had a diagnosis of dementia was conducted using the Australian legal case law search engines Austlii and BarNET JADE from 17 July 2022 to 30 August 2022, covering the periods from 1986 (Australian Capital Territory), 1992 (New South Wales), 1994 (Queensland), 1977 (South Australia), 1985 (Tasmania), 1994 (Victoria) and 1964 (Western Australia) to August 2022. In addition, individual state supreme court case lists were separately searched by two of the authors (SR and AW) when these were provided. We used the search terms ‘Alzheimer’s’, ‘dementia’, ‘Lewy body’, ‘frontotemporal’ ‘neurocognitive disorder’ and ‘Huntington’s’. Cases were then individually reviewed for inclusion. We specifically excluded cognitive impairment or cognitive decline that were not diagnosed as crossing the threshold for dementia and neurocognitive disorders that were solely due to head injury in order to maintain a focus on dementia. These case lists and repositories do not contain all historical decisions for every jurisdiction and only provide decisions that have been made public by the courts. Therefore, the number of unpublished cases involving an offender with dementia could not be established.

Data were collected based on the most serious offences according to the Australian and New Zealand Standard Offence Classification (ANZSOC; Australian Bureau of Statistics, 2011) if there were multiple charges. Actuarial variables such as the ages and genders of the offenders and victims were sought, as well as the circumstances of the crimes, relationships of victims to offenders, dementia types, any criminal history and the final charges and outcomes of the judicial processes. We excluded historical crimes – that is, crimes where the accused committed the alleged offence many years previously – as the accused might not have had a dementing illness at that time. These were usually child sexual assault crimes.

Dementia type was based on the clinician reports quoted in the cases, which included clinical findings and often references to cerebral imaging results. In cases where no dementia subtype was specified, a dementia subtype was determined using Diagnostic and Statistical Manual of Mental Disorders (5th ed.) (DSM-5) criteria (American Psychiatric Association, 2013) for neurocognitive disorders (dementias) on the basis of the published neuropsychological and other clinical findings by the two authors of this study with clinical expertise in dementia (SR and AW) who were each blinded to the other’s opinion. If a consensus could not be reached or if no neuropsychological findings were published, cases were relegated to the ‘unknown’ category.

Cases were said to be related to executive dysfunction based on neuropsychological findings in the text of the cases or dementia diagnoses (e.g. behavioral variant frontotemporal dementia, where executive dysfunction is an early and prominent feature of the condition; see Bang et al., 2015).

The Modified Monash Model (Australian Government Department of Health & Aged Care, 2021) was used to classify locations as either cities (MM1) or regional and remote areas (MM2 to MM5).

Results

Overall, we identified 62 offenders whose offences occurred between 1995 and 2020.

Diagnoses were made by medical and psychological expert witnesses and/or treating medical practitioners. Of the professions referred to (n = 98), most were psychiatrists (59.18%) followed by neuropsychologists (20.41%). Diagnoses were also made by neurologists (9.18%), psychologists (7.14%) and geriatricians (4.08%).

Gender

Most of the offenders were male (n = 56; 90.32%), with 6 females (9.68%).

Age at time of offence

In 4 of the cases reviewed, the age of the offender was unknown. Of the 58 whose age was reported, the median age was 68.5 years (range = 27 to 88 years). Those with Huntington’s disease were younger (range = 27 and 48 years), as were those with substance-use-related dementias (range = 43 to 60 years). People diagnosed with frontotemporal dementias were aged between 55 and 86 years, whereas all of those with Alzheimer’s dementia were aged over 65 years and all but one who had a vascular component to their dementia (including those with mixed vascular and Alzheimer’s dementia) were aged over 62 years (with the exception being aged 52 years).

Geographical location of offence

Of the 53 known locations, 32 offences occurred in a city (60.38%) and 21 occurred in rural or remote regions (39.62%). A total of 9 locations were not specified.

Dementia type

The most common subtype of dementia was vascular dementia (19.35%), followed by frontotemporal dementia (16.13%; see Table 1). Unknown dementias form 17.47% of the total. Of the offenders, approximately one third (35.48%) had a vascular component to the dementia.

Table 1. Distribution of dementia subtypes and mean ages of offenders.

Dementia type	Frequency (%)	Mean age in years (range)
Vascular dementia	12 (19.35%)	72.92 (62–87)
Unknown/other	10 (16.13%)	66.89 (34–86)
Frontotemporal dementia	10 (16.13%)	67.00 (55–86)
Dementia due to alcohol/other drugs	8 (12.90%)	49.86 (43–60)
Mixed vascular and Alzheimer’s dementia	7 (11.29%)	79.86 (65–88)
Alzheimer’s dementia	6 (9.68%)	77.00 (65–86)
Huntington’s disease	4 (6.45%)	36.35 (27–48)
Mixed vascular and alcohol-related dementia	3 (4.84%)	67.67 (64–87)
Dementia with Lewy bodies	1 (1.61%)	56.00 (56)
Posterior cortical dementia	1 (1.61%)	60.00 (60)
Total	62	66.15

A total of 47 offenders had dementia subtypes that are characterized by executive dysfunction and/or had this deficit specifically mentioned as part of neuropsychological testing (74.6%).

Offence type

We examined the most serious offences, most of which involved violence, such as sexual assault, assault and murder (n = 54, 87.10% of cases). Both driving offences were serious and resulted in death (Table 2).

Table 2. Frequency of dementia subtype by most serious offence charge (for most serious criminal charge against each offender).

	Mixed vascular and Alzheimer’s dementia (n = 7)	Dementia due to drugs/alcohol (n = 8)	Alzheimer’s dementia (n = 6)	Vascular dementia (n = 12)	Mixed vascular and alcohol dementia (n = 3)	Huntington’s disease (n = 4)	Unknown /other (n = 10)	Frontotemporal dementia (n = 10)	Dementia with Lewy Bodies n = 1	Posterior cortical atrophy n = 1
Homicide	6 (85.71%)	4 (50.00%)	2 (33.33%)	3 (25.00%)	1 (33.33%)	0	0	4 (40.00%)	0	1 (100%)
Child sexual assault (CSA)	0	0	3 (50.00%)	5 (41.67%)	2 (66.67%)	0	5 (50.00%)	2 (20.00%)	0	0
Assault/cause injury	1 (14.29%)	3 (37.50%)	0	2 (16.67%)	0	0	0	2 (20.00%)	1 (100%)	0
Adult sexual assault	0	0	1 (16.67%)	2 (16.67%)	0	1 (25.00%)	1 (10.00%)	2 (20.00%)	0	0
Property & larceny	0	0	0	0	0	2 (50.00%)	1 (10.00%)	0	0	0
Driving offences	0	1 (12.50%)	0	0	0	0	1 (10.00%)	0	0	0
Arson	0	0	0	0	0	1 (25.00%)	0	0	0	0
Breach of conditions	0	0	0	0	0	0	1 (10.00%)	0	0	0
Perverting the course of justice	0	0	0	0	0	0	1 (10.00%)	0	0	0

A total of 19 records did not mention whether or not the accused had been found guilty of a criminal offence (30.65%), and of those that did record this factor (n = 43, 69.35%), 26 offenders did not have a criminal history (60.47%). Just 1 of the 7 offenders accused of adult sexual offences whose histories were known had committed similar offences (14.29%), as had 4 of the 7 offenders with a known criminal history who were charged with assault (57.14%). Just 1 of the 3 offenders charged with property or larceny had a history of similar offences (33.33%). Of the 21 cases involving homicide, 9 did not include the offender’s criminal history (42.86%), and of the 12 cases where the histories were known, only 2 offenders had past charges (16.67%), with 1 fined for a non-violent offence. In contrast, of the 12 child sexual assault cases, 5 offenders whose criminal history was available had previous child sexual assault charges that predated their dementia diagnosis (41.67%), and 1 offender had pending charges for similar offences.

Of those who had committed previous offences, 1 offender had a history of uncomplicated vascular dementia and 2 offenders had a diagnosis of Alzheimer’s disease, both of whom were charged with child sex offences. The remainder had diagnoses of alcohol-related dementia, frontotemporal dementia and Huntington’s disease. Of the 4 offenders diagnosed with Huntington’s disease, 3 had a previous criminal history characterized by repeat offending over a period of years, including violent, traffic and larceny offences.

With respect to dementia subtype, 46 offenders had conditions that are characterized by early executive dysfunction (74.19%), namely substance use-related dementias, subcortical vascular dementia, frontotemporal dementias and Huntington’s disease. In most cases, executive dysfunction was mentioned as relevant to the offending. Of interest, mentions of executive dysfunction was lowest in the group accused of child sex offences (n = 9, 52.94%), compared to 18 of those charged with homicide (85.71%).

Victim demographics

Of the 96 victims, 50 were female (52.08%) and 15 were male (15.62%). Gender was not listed for 31 of the victims (32.29%), of whom 21 were casualties of a single event caused by a driver who was later charged with the dangerous operation of a vehicle (67.74%).

Relationship to victim

A total of 5 offenders committed crimes without a direct victim, including vehicular damage, stealing, breach of a supervision order and perversion of the course of justice.

Of the offences that did involve a victim, most of the offenders were known to the victim (n = 47, 82.46%). A total of 17 offenders were or had been in an intimate relationship with the victim, 15 of whom killed their victim. All of the victims who were killed were known to the offender, and although generally younger than the offender, the age difference was less than 10 years in all but one case.

Sexual offenders’ relationships with their victims differed according to the age of the victim. Of those who committed childhood sexual abuse (n = 16), most were known to their victims (n = 13, 81.25%). In 2 cases the relationship was unable to be determined and in 1 case the victim and offender were not known to each other. In contrast, of the adult sexual offending cases (n = 7), most of the offenders were not known to the victim (n = 4, 57.14%), and the case summaries indicate that these offences were opportunistic. These differences are more likely to reflect typical offender typologies rather than being specific to older offenders (Simons, 2017).

Sentencing

As might be expected in a population with dementia, most of the offenders were found to be either lacking the capacity to stand trial (unfit to stand trial) or not guilty by virtue of their cognitive impairment (n = 42, 67.74%). Just 1 case was dismissed due to dementia, and only 2 offenders were judged fit to stand trial with the issue of capacity not being raised. Dementia was cited as a cause of substantial impairment in 4 cases where the original charge was murder, 1 charge of damage property was dismissed and dementia was cited in sentencing reasons in 15 cases.

Of those charged with adult sexual offences, 1 offender submitted a legal appeal because his cognition was not raised in the initial trial but the appeal was dismissed on legal grounds. Just 1 offender was already deemed to not have capacity and was charged with breaching supervision orders, and in 1 case the outcome was not provided. Just 1 case of adult sexual assault discussed the offender’s intent with respect to the circumstances of the crime, 3 offenders were found to not have capacity to stand trial and 2 offenders had their sentence reduced as a result of the contributing cognitive impairment.

With respect to child sexual abuse, in 11 of the 16 cases (68.75%) the offenders were either considered unfit to stand trial (n = 10) or not guilty as a result of their mental condition (n = 1).

A total of 17 of the 21 offenders charged with homicide (80.95%) were found to be lacking the capacity to stand trial or not guilty by reason of their cognitive impairment, while the others had their charges reduced to manslaughter and their sentences reduced by virtue of consideration of substantial cognitive impairment at the time of the offence.

Discussion

Most of the offenders in the present sample were male, consistent with other studies of criminal offending in Australia (Beatton et al., 2018; Broidy et al., 2015). The median age in our study is 68.5 years, an age group (65+) that accounts for 2% of people who have had crimes proceeded against them by the police (Australian Bureau of Statistics, 2023).

The geographical distribution of the offenders differs from the distribution of the Australian population. Although most of the offences occurred in metropolitan areas, almost 40% occurred in regional or rural localities. According to the Australian Institute of Health and Welfare (2022), as of 7 July 2022, 72% of Australians resided in major cities. The greater than expected rate of offending in non-metropolitan areas mirrors the geographical distribution of people charged with crimes across all age groups (Allard et al., 2013) and could reflect lack of access to services (Carcach, 2000). Further examination is required to determine whether or not access to diagnosis and management of cognitive impairment is a potential modifiable factor in the 65+ age group.

Overall, there is a comparative underrepresentation of cases in this database involving people with Alzheimer’s dementia (9.53%). Worldwide, Alzheimer’s dementia accounts for 60% to 70% of dementias and vascular dementia for about 20% to 30% (Fratiglioni et al., 1999), while dementia with Lewy bodies accounts for about 4.2% of community diagnosed dementias (Jones & O’Brien, 2014), frontotemporal dementia for about 2.7% of cases of dementia (Hogan et al., 2016) and alcohol-related dementias for about 1.4% of dementia patients admitted to Australian hospitals (Ridley et al., 2013).

The prevalence of Huntington’s disease was estimated to be 6.29 per 100,000 in New South Wales in 1996 (McCusker et al., 2000), 12.10 per 100,000 in Tasmania in 1990 (Pridmore, 1990) and 8.00 per 100,000 in Victoria in 1999 (Tassicker et al., 2009), while a meta-analysis of 10 studies from North America, Europe and Australia demonstrates an overall prevalence of 5.70 per 100,000 (Pringsheim et al., 2012). Based on these figures, the number of people with diagnosed Huntington’s disease in the present study (6.45% of the sample) greatly outnumbers the prevalence of the condition in the community, consistent with research indicating an increased prevalence of offending in people with the condition (Jensen et al., 1998). We found that the increase in offending in our study was limited to males, and although our numbers are small, we note that 1 of the 4 offenders with Huntington’s disease in our sample was a female.

The moniker ‘executive function’ is an umbrella term encompassing higher-order cognitive processes involved in goal-directed and future-oriented behaviors, including attention, planning, judgment, self-monitoring, inhibition and problem-solving (Salthouse, 2005), and it has been linked to violent and aggressive behavior (Brower & Price, 2001). Although these cognitive domains involve brain systems that are not based in a single anatomical location, the prefrontal cortex is intimately involved in executive function, an area that is the primary site of dysfunction in frontotemporal dementia (Perry & Rosen, 2016) and that is thought to be related to the association between frontotemporal dementia and criminal behavior (Berryessa, 2016; Brower & Price, 2001; Mendez, 2010, 2022; Mendez et al., 2005).

Our results suggest that violent crime committed by older people with dementia is largely driven by executive dysfunction rather than a specific dementia type, leading to a preponderance of crimes committed by people with frontotemporal dementia, subcortical vascular dementia, Huntington’s disease and alcohol- and substance-use-related dementias. Like other research, we also found that dementia types characterized by prominent executive impairments were common amongst all crime types. Although other studies have focused on less serious criminal behaviors (Liljegren et al., 2015, 2019), our study indicates that executive dysfunction is also present in more serious and violent crime.

Executive impairments are also prominent in both Huntington’s disease (Ho et al., 2003; Larsen et al., 2015; You et al., 2014) and vascular dementia (Charlton et al., 2006; Schmidtke & Hüll, 2005), whereas the hallmark of early Alzheimer’s disease is memory disturbance. People with Alzheimer’s dementia demonstrate impairments of certain executive functions such as working memory, but these tend to occur later in the disease (Lindau et al., 2000) and are posited to occur secondary to the memory impairment of the early stages (Stopford et al., 2012). It is possible that the posterior-mediated executive dysfunction might not affect the domains that result in problem behaviors until later in the disease.

It is, however, likely that criminal behaviors in dementia are not solely attributable to executive dysfunction. Rather, it may be the case that certain cognitive functions in combination with executive dysfunction promote or inhibit risk of criminal behaviors. For instance, people with frontotemporal and other dementias that affect the prefrontal cortex have additional executive impairments of disinhibition (Ramanan et al., 2017) and social cognition (Lindau et al., 2000) that are likely to impact on their judgment of appropriate behaviors and interpretations of social situations, rendering them at greater risk of offending. Gender is likely to play a role too, as the males outnumbered the females in our sample, mirroring non-demented criminal populations. A study of people with Huntington’s disease similarly found that, unlike males, affected females did not have an elevated risk of offending compared to their first-degree relatives (Jensen et al., 1998).

Furthermore, there are subtypes of cognitive domains. For instance, apathy – which occurs in Alzheimer’s, vascular and frontotemporal dementias – has several different forms (Robert et al., 2009), and is associated with different behaviours depending on dementia type (Chow et al., 2009). Apathy is associated with impulsivity and compulsive behaviour in frontotemporal dementia, and with depressive symptoms in people with Alzheimer’s disease (Chow et al., 2009, Tagariello et al., 2009). Thus, the use of cognitive assessment to determine the risk of reoffending requires close attention to the particular domain assessed as well as the combination of cognitive impairments.

An unexpected finding is the low numbers of cases involving people diagnosed with dementia with Lewy bodies, with only one case diagnosed in the present study. Dementia with Lewy bodies classically manifests with executive, attentional and visuospatial deficits, hallucinations and delusions. Psychotic features are known to be a factor in the commission of offences (Yee et al., 2020), particularly violent offences (Fazel et al., 2009) and repeat offending (Fazel & Yu, 2011). The epistemological conclusion is that the combination of executive impairment and psychotic features seen in dementia with Lewy bodies would confer a greater predisposition for the commission of offences. Although misdiagnosis is a possible explanation for the lack of such cases identified in our search, another possibility is that other clinical features might reduce the risk of offending in the case of dementia with Lewy bodies and Parkinson’s plus syndromes, for instance mobility restrictions and visual impairment.

Our finding that most murder victims were killed by their partner is consistent with previous research (Bourget et al., 2010; Reutens et al., 2015). In contrast to the findings of Talashati et al. (2021), the homicides in our sample were committed by people with a range of dementias, not just frontotemporal dementia, consistent with previous research on older homicide offenders (Reutens et al., 2015). Only one homicide case in our study appeared to have had an element of planning, where a man had threatened to kill his former partner and then, after a later confrontation, shot her. In 8 cases the offender’s state of mind could not be determined because of their cognitive impairment, while 11 unplanned homicides occurred in the setting of an angry reaction to an argument or to perceived behavior. Similarly, the assault, arson and motor vehicle cases appeared to be impulsive in nature. Although the numbers in our sample are small, our finding that people with Huntington’s disease committed varied crimes at the lower end of the severity scale is consistent with previous research (Jensen et al., 1998).

In the present study, offending involving the same offence was found to be uncommon, with the exception of those charged with child sex offences, where repeat offending of the same crime type occurred with the index offences predating a dementia diagnosis. This suggests that dementia has less of an effect on the commission of this particular crime type than the offenders’ underlying drives.

Repeat offending is also noted in 3 of the 4 offenders with Huntington’s disease in our sample, which may be related to their relatively young age or the pattern of progression of cognitive impairments in other forms of dementia that may differentially impact on factors required for the commission of offences, including frailty, mobility, memory and reaction speed. Further research is required to determine the factors, if any, that inhibit recidivism.

Determination of risk factors for the commission of crime by elderly people is of importance because the commonly used violence risk assessment tools have not been developed with older people in mind, nor do they take into account the neurobiological and clinical features of dementia subtypes that might be involved in the commission of an offence. Similar to Kratcoski’s (1990) study of elderly homicide offenders, we found that the preponderance of homicides involved an intimate partner and occurred as an unplanned angry reaction to the victim’s behavior or in the context of an argument.

In cases where the offender has committed a crime that is causally related to their cognitive impairment, currently available risk assessment tools are less useful for the assessment of recidivism. Overall, the risk of repeat offending in an individual with dementia will be related to multiple physical, psychiatric and cognitive factors. For instance, changing behaviors and increasing physical impairments over the course of the illness combined with the pattern of cognitive decline are likely to mitigate criminogenic potential in most cases of dementia. Caution is necessitated when devising risk assessment tools or highlighting risk in individuals with dementia due to the dynamic and deteriorating course of the illness impacting extrapolations from any putative associations based on cross-sectional data.

It is important to bear in mind that the number and types of cases in the present study might arise from the court system in Australia relying on lawyers to request a cognitive assessment if there is no indication that the alleged offender has a diagnosis. This raises an important question about the availability of cognitive assessment for older people accused of committing violent crimes. Given the potential loss of freedoms involved, screening for cognitive impairment in all older accused offenders prior to trial would ensure greater equity of justice and assist legal professionals with making better judgments as to which of their clients might be suffering from cognitive decline and require further expert assessment.

Limitations

The strengths of this study include the offenders having been diagnosed by clinicians, often with additional brain imaging available to underpin their clinical diagnosis. It should also be noted that the cases do not represent the totality of offences as they were drawn from published cases from higher courts and not all cases are reported.

We relied on the dementia diagnoses made by expert witnesses and/or their findings of executive dysfunction, thus the method of diagnosis was not standardized. The lack of a control group of people without dementia limits the conclusions that can be drawn from this study and is a suggestion for future work in this area.

The inability to undertake a definitive neuropathological diagnosis is a relative weakness that impacts on all clinical dementia research. The study is also limited to published cases, thus excluding less serious offences – consequently, the clinical profile of less serious offences might differ from that presented herein.

Conclusion

The offenders with dementia in this study were found to have a tendency to commit crimes that are related to underlying executive dysfunction. The numbers of offenders in this age group are small, and consequently other factors are likely to be involved in the commission of crimes or protective against offending. Future research is required to determine these additional characteristics, which would be helpful for determining sentencing, release and post-release accommodation planning. This is likely to differ not only with respect to the underlying dementia subtype but also the type of offending and any comorbid medical conditions.

From a justice perspective, screening for cognitive impairment is a feasible prospect given the relatively low numbers of elderly people accused of committing crimes and the marked difference in outcome between receiving a typical sentence and having one’s charges downgraded, being given a reduced term or being found not guilty due to mental illness. Ideally, such screening would occur relatively soon after an elderly or older person is arrested so that a relationship between the offending and any cognitive impairment can be determined with greater certainty.

Ethical standards

Declaration of conflict 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.