Introduction

The criminal justice system in most Western countries plays an important role in public safety, enforcing laws, and protecting people’s rights. This complex system is comprised of separate but interrelated phases of involvement, including contact with police services, court, correctional facilities, and community re-entry services (e.g., probation/parole supervision) [1]. In addition, each phase of the criminal justice system has different professionals, each with different roles and responsibilities [1]. To ensure that justice is served, professionals in the criminal justice system must balance the need to sanction those who commit crimes (i.e., crime control) with ensuring that this process is fair and protects individual rights (i.e., due process) [2].

International research has established that persons with intellectual/developmental disabilities (IDD) experience barriers throughout the criminal justice system that may compromise justice in their cases. For example, these individuals experience limited understanding of legal terms and processes [3], barriers to communicating with their legal representation [4], and are more likely to self-incriminate without understanding the implications of their actions [5]. Justice professionals may also experience difficulties recognizing persons with IDD and providing appropriate accommodations to participate in justice processes when needed [6]. Combined, these results suggest that persons with IDD face a higher risk of criminalization and poorer outcomes in the criminal justice system than those without IDD [7].

Article 13 of the Convention on the Rights of Persons with Disabilities (CRPD) seeks to address these risks by outlining the responsibilities of countries to ensure that people with disabilities (including IDD) have equal access to justice as those without disabilities [8]. This includes providing accommodations for persons with disabilities involved in the justice system that facilitate participation in processes and training for justice professionals regarding how to provide appropriate accommodations for disabilities [8]. Many countries have developed policies, programs, and interventions that ensure persons with disabilities are provided accommodations at various points within the criminal justice system; however, a formal review of the peer-reviewed literature describing these policies, programs, and interventions has yet to be conducted.

This scoping review aims to fill a gap in the literature by summarizing the availability of evaluated programs and interventions for providing accommodations to all persons with IDD and training to justice professionals regarding IDD at each phase of the criminal justice system, namely, during police interactions, court involvement, incarceration, and community re-entry (e.g., probation/parole). Previous scoping reviews have examined interventions for persons with IDD involved with the criminal justice system. These studies examined the interactions between persons with specific disorders (e.g., autism spectrum disorder) and the criminal justice system [9•] or the interventions for persons with IDD at one point in the criminal justice system (e.g., police contact) [10•]. One literature review provided an overview of issues facing persons with IDD in the criminal justice system, including assessment and intervention and treatment approaches; however, it did not report using a formal knowledge synthesis method [11•]. This scoping review builds on previous knowledge syntheses [9•, 10•, 11•] about the justice involvement of persons with IDD by (i) focusing solely on the programs intended to improve the ability of persons with IDD to participate in the criminal justice system and (ii) focusing on peer-reviewed articles that describe these programs for all persons with IDD (rather than one subgroup of persons with a specific diagnosis). This scoping review was informed by three questions:

  1. 1)

    For each key phase of the criminal justice system, what programs and interventions to provide accommodations to persons with IDD or training to justice professionals regarding IDD have been described in the peer-reviewed literature?

  2. 2)

    What are the characteristics of the research being conducted on the programs and interventions for persons with IDD in the criminal justice system?

  3. 3)

    What are potential future avenues of research and intervention for persons with IDD involved in the criminal justice system as per the main findings of this review?

Methods

Scoping reviews are conducted for numerous reasons: to examine the characteristics (e.g., extent and range) of research activity about a given topic, to summarize recent research findings about a particular topic, and to identify gaps in existing literature [12, 13]. For this review, Arskey and O’Malley’s methodological framework for conducting scoping reviews was used, including the following stages: (1) develop a research question, (2) develop a search strategy for identifying relevant studies, (3) search for studies in relevant databases, (4) select studies according to inclusion/exclusion criteria, (4) chart the data thematically, and (5) summarize the results [12].

Search Strategy and Inclusion/Exclusion Criteria

A broad search strategy was developed by combining search terms related to intellectual and developmental disabilities, labels ascribed to persons involved in the criminal justice system (e.g., “witness” and “offender”), and each of the key phases of the criminal justice system (e.g., “law enforcement” and “court”). These search terms were combined during the search using Boolean operators (e.g., AND, OR) and database search tools. The following databases were searched in May 2022: PsycINFO, Proquest, Social Sciences Citation Index, and Criminal Justice Abstracts. The terms used for the search strategy and results for each database can be found in Appendix A.

Search results were limited to peer-reviewed publications: (a) written in English, (b) published between January 2008 and search date (May 2022), (c) clearly described their methodology (e.g., quantitative, qualitative, and mixed methods), and (d) focused on a program or intervention for persons with IDD or justice professionals at one of the key phases in the criminal justice system. This timeframe was selected to capture articles published since Jones’ literature review about intellectual disabilities and the criminal justice system in 2007 [11•]. The term learning disability was included in the initial search of databases, given that this label may be used to describe developmental disabilities in the UK. Articles that referred to learning disabilities were screened for location in later stages, and articles conducted outside of the UK that described learning disabilities were removed. Table 1 outlines the inclusion/exclusion criteria used to evaluate articles at each review stage.

Table 1 Inclusion/exclusion criteria
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Covidence is a web-based collaboration software platform designed to structure and streamline the processes associated with knowledge synthesis [14]. This software was used to help remove duplicate results, screen titles and abstracts, complete full-text reviews, and perform data extraction. As illustrated in Fig. 1, all database search results were imported into the platform, and 5675 duplicates were removed by the Covidence program.

Fig. 1
figure 1

PRISMA flow diagram

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In the initial screening phase, 15 randomly selected articles were reviewed by the first three authors together using the inclusion/exclusion criteria in Table 1 and an agreement of 93.3% between these authors was achieved. The remaining 8490 articles were divided evenly among the first three authors, and each article’s title and abstract were reviewed independently using the same inclusion/exclusion criteria. This initial screening phase resulted in 288 articles.

The first three authors then completed a full-text review of the remaining 288 articles, which were reassessed using the same inclusion/exclusion criteria used in the initial phase. In addition, a quality assessment was also completed to ensure that the article included (a) research objectives and/or questions, (b) a complete method section (e.g., described participants, description of the intervention, data analysis), and (c) results. For articles that described individuals with learning disabilities, the authors also ensured that the research was conducted in the UK and articles describing learning disabilities in other countries were excluded. Each article was independently reviewed by two members of the team. For the articles with reported conflicts regarding inclusion (n = 12), the team met to review the articles together using the inclusion/exclusion criteria and to determine whether they should be included. Following this full-text examination, 22 articles remained.

Analysis

Information from each study was extracted in Covidence using a form that guided the reviewers to identify specific items from the articles. These items became the columns in the table used for analysis and summary. Studies were organized in rows according to which phase in the criminal justice system they addressed. There were some studies that addressed multiple phases of the criminal justice system (e.g., interviewing in police custody and court) and these articles were put in the earliest phase that the intervention might be used. Table 2 presents the information for the 22 included articles.

Table 2 Description of articles included in scoping review (2008–2022)
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Results

Characteristics of Studies

With regard to the research methodology and design used in the studies included in the analysis, eleven (50%) of the 22 studies were quantitative, six (27%) studies were qualitative, four (18%) studies combined quantitative and qualitative methods, and one (5%) study used a single-case design. Most studies were conducted in the UK and Australia.

For the studies that included qualitative assessments (i.e., qualitative studies and combined methods studies), most studies [15, 16, 18, 19, 23, 24, 26, 34] focused on the perspectives of the professionals involved in the programs. Only three studies [18, 22, 23] included the perspectives of persons with IDD involved in the criminal justice system. One study [29] used a case study approach to explore the cost–benefit of different court outcomes for one individual. For the combined methods’ studies, the data was collected using questionnaires and surveys that included both Likert scales and free-text responses. Four quantitative studies used secondary analysis of administrative data [25,26,27, 30]; three studies used a descriptive design; two studies used an experimental design with a comparison group [21]; and one study used a pre-post design [31]. One study used a single-case multiple baseline design to evaluate the effect of performance-based instruction.

Study Findings

Most studies focused on earlier stages in the criminal justice system, namely police contact and court proceedings. The number of studies examining accommodations for persons with IDD or training for justice professionals decreased in later phases of the criminal justice system (e.g., eleven studies for police contact v. one for community re-entry). Nineteen (86%) of the studies focused on providing accommodations to individuals with IDD involved in the justice system [16, 18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34], whereas 2 (9%) focused on training justice professionals about developmental disabilities [15, 17]. One study focused on both accommodations for persons with IDD involved in the criminal justice system and training for law professionals.

Eleven (50%) of the 22 studies focused on providing accommodations to persons with IDD or training to justice professionals during police contact. One study identified that a screening tool successfully identified persons with IDD in police custody [20]. Two studies identified that training could improve police officers’ interactions with persons with IDD [15, 17]. Four studies found that using a third-party support person during police interviews provided good support with communication and advocacy, though the voice of persons with IDD largely remained absent [16, 18, 19, 24]. Four studies found that modifications to police processes (e.g., interviews and cautions) could successfully be used to improve communication with persons with IDD [21,22,23].

Six (27%) of the studies focused on providing accommodations to persons with IDD or training to justice professionals during court proceedings. Five of these studies focused on the benefits of diverting persons with IDD to mental health courts that provide trained staff and that seek to address the underlying issues contributing to the commission of an offence [25,26,27,28, 30]. One study found that adding a team of clinicians that specialized in neurodevelopmental disorders helped detect diagnoses and reduce custodial remands for persons with IDD [27]. Finally, one unique study identified the cost benefits of using a Disability Justice Support Program over finding a person with IDD unfit to stand trial or a guilty plea [29].

Four (18%) studies focused on providing accommodations to persons with IDD or training to justice professionals in correctional facilities. Three of these studies focused on developing adequate screening protocols that could inform referrals to specialized interventions if they were available [32, 33]. One of these studies found that providing a team of specialized clinicians helped to make clinically useful observations and referrals [32]. One study identified that providing an adapted sexual offender treatment program in a correctional facility for persons with IDD had the same outcomes on measures of victim empathy and social intimacy as the one provided to persons without IDD and positively impacted recidivism 16 months after release [31].

One (5%) study focused on accommodations for persons with IDD during community re-entry (e.g., probation/parole). This study reported on the benefits and challenges of a Custodial Partnership Group that planned for community support post-incarceration [34].

Discussion

Article 13 of the CRPD seeks to ensure that persons with disabilities (including IDD) have equal access to justice as those without disabilities. It suggests that this is accomplished by providing accommodations for persons with disabilities involved in the justice system that facilitate participation in processes and training for justice professionals regarding how to provide appropriate accommodations for disabilities [8]. This scoping review aimed to examine the peer-reviewed literature describing accommodations for persons with IDD and training to justice professionals regarding IDD at key phases of the criminal justice system.

Overall, this review indicated that there are several innovative programs intended to improve the ability of persons with IDD to participate in the criminal justice system and to assist justice professionals in recognizing and providing accommodations. Most of the peer-reviewed literature included in this scoping review focused on screening and intervention in earlier phases (e.g., police contact and court proceedings), which suggests that efforts are being made earlier in the criminal justice system to identify and divert persons with IDD to more appropriate services and opportunities [15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30]. This is consistent with the Sequential Intercept Model (SIM), which identifies that recognition and intervention in earlier phases of the criminal justice system can play an important role in reducing the disparity experienced by overrepresented groups, such as persons with IDD [35].

The peer-reviewed literature in this scoping review focused on four common areas: screening, third-person assistance, communication assistance, and diversion. The first area of peer-reviewed articles focused on developing reliable and valid tools to detect persons with IDD [20, 32, 33]. Screening provides an important opportunity to identify persons with IDD at all the key phases of the criminal justice system and subsequently provide accommodations or necessary referrals for support and services. The benefits of using screening tools are that they can be administered by justice professionals with minimal training and can be used to triage persons with IDD to other programs and services, including a more thorough assessment of cognitive and adaptive abilities [33]. One of the limitations identified with screening was that it did not always translate into appropriate accommodations being provided to persons with IDD [20]; therefore, it may be helpful to develop tools that provide clear direction for justice professionals about the next steps after screening. Finally, given that many of the services (e.g., appropriate adult, mental health courts) are “opt-in” and the individual needs to be known as having an IDD to qualify [16, 26], it is important to recognize that screening plays an important role in ensuring that persons with IDD have access to the other resources intended to ensure equal access to justice.

The second area that peer-reviewed articles focused on was providing third-party assistance to persons with IDD and criminal justice professionals. These programs provide an intermediary person who assists the person with IDD by advocating on their behalf and ensuring that appropriate accommodations are being provided and that assists justice professionals by providing information about IDD and ensuring comprehension [16, 18, 19, 24]. While justice professionals and persons with IDD reported valuing assistance from the intermediaries, there was debate about whether the person should be a familiar person (e.g., a family member) or an impartial volunteer or professional [16, 18]. The peer-reviewed literature also described the inclusion of interdisciplinary teams specialized in IDD that provide assessments, interventions, and/or referrals [27, 32]. The results from these studies suggested that having the support of an interdisciplinary team provided a more nuanced approach to ensuring justice by being able to recognize the presence of dual diagnosis [27]; however, it is also important for these professionals to be familiar with the criminal justice system to be able to recognize the impact of the environment on the individual [32]. Therefore, considerations for training should not only focus on increasing the knowledge and abilities of both justice professionals about IDD but also on increasing the knowledge of experts in IDD about the criminal justice system.

The third area that peer-reviewed articles focused on was adapting existing processes or developing new processes that assisted justice professionals in communicating during and about the complex processes of the criminal justice system [21,22,23]. As Parsons and Sherwood [23] identified, how information is shared can result in disempowerment from lack of knowledge and increase the stressful nature of custody. The peer-reviewed articles in this scoping review indicated that adapting the interview processes and how information was provided could improve the recollection of relevant information [21] and be integrated into the standardized processes [22]. In addition, some research identified that psychological interventions and education provided in correctional facilities could be adapted to address the needs of persons with IDD [31, 34]. Ideally, persons with IDD are diverted from the criminal justice system before incarceration; however, for those who are incarcerated, it is important for them to have access to programs and interventions that may improve community re-entry and recidivism both directly (e.g., employment) and indirectly (e.g., housing) [36, 37]. Case conferencing mechanisms, such as the Custodial Partnership Group [34], may provide a collaborative opportunity to engage with the incarcerated person with IDD and community agencies during incarceration to plan and prepare for community re-entry.

The final area that peer-reviewed articles focused on was finding opportunities to divert persons with IDD away from the criminal justice system [20, 32, 33]. The international proliferation of problem-solving courts has resulted in the opportunity to divert groups of individuals away from the criminal justice system to community-based services that can address the underlying issues contributing to the commission of an offence [25, 26, 28, 30]. These courts are staffed with knowledgeable professionals that have a different understanding of the unique needs of these individuals and are more likely to suggest sentences that do not include incarceration [30]. Persons with IDD typically are diverted to mental health courts (a type of problem-solving court); however, as Chaplin and colleagues identified, these courts may still struggle with supporting persons with IDD and providing specialized services for persons with IDD within the mental health court setting may provide further benefits beyond what is typically experienced [27].

Finally, several studies identified the importance of providing formal training for justice professionals to ensure they can recognize persons with IDD and engage in responses accordingly. While none of the peer-reviewed articles in this review described a formal training program, these studies highlighted the importance of ensuring that justice professionals can understand how different disabilities (e.g., autism, fetal alcohol spectrum disorder) may result in different patterns of impairments that will affect these individuals in different ways [24] and should provide an opportunity for justice professionals to rehearse with feedback [17].

Gaps in Literature

In this scoping review, we identified several gaps in the literature on the accommodations to persons with IDD or training to justice professionals regarding IDD. One of the most significant gaps in the peer-reviewed literature was the near absent voice and perspectives of persons with IDD. Only three peer-reviewed articles solicited the perspectives and insights of persons with IDD about the accommodations being provided [18, 22, 23]. Article 3 of the CPRD provides the foundation in which the other articles, including Article 13 — Equal Access to Justice — should be exercised, namely, through equal opportunity, non-discrimination, and “full and effective participation and inclusion in society” [8]. Therefore, it is important that the perspectives of persons with IDD are included in the development and evaluation of programs intended to provide accommodations and ensure equal access to justice. Future research regarding accommodations should incorporate the perspectives of persons with IDD. In addition, as has been identified elsewhere [38], training for justice professionals should include persons with IDD as trainers.

The second identified gap in the peer-reviewed literature was the apparent lack of continuity in communication about persons with IDD between the key phases of the criminal justice system and ensuring that information follows them to promote consistent support in later phases of the criminal justice system. It may be helpful for future interventions and research to focus on how information about persons with IDD is communicated between the stages of the criminal justice system or the impact of having a consistent intermediary person who can help advocate and communicate information about persons with IDD at each phase of the criminal justice system. In addition, research comparing training to justice professionals about IDD to providing third-party assistance (e.g., appropriate adult, neurodevelopmental disability specialist services) may also help to identify the strengths and limitations of each approach. As McCausland and colleagues [29] identified, providing strategic support that enables persons with IDD to participate in court proceedings provided cost savings and improved the timelines and quality of outcomes for persons with IDD.

The final identified gap in the peer review literature was the lack of studies focusing on providing accommodations during community re-entry. In this scoping review, only two studies examined the accommodations for persons with IDD and training provided to probation and parole officers about IDD during community re-entry [34]. Given that discharge without disability support services has been linked to recidivism, administrative offences resulting from breaching probation or parole, and frequent use of hospital resources [39,40,41], it is important to consider what accommodations are needed for persons with IDD and training for probation and parole officers to increase the success of community re-entry for persons with IDD.

Limitations

While this study provided a rigorous evaluation of the accommodations provided to persons with IDD in the criminal justice system and training to justice professionals about IDD, some limitations were noted. The first limitation of this review is that a search of the grey literature and non-English publications was not included. As a result, there may be programs being offered within the criminal justice system for persons with IDD or training provided to justice professionals that were not captured in this review. Similarly, this study focused on the formal programs to provide accommodations for persons with IDD in the criminal justice system. It is possible that there are informal accommodations being provided by justice professionals that are being captured in the literature describing their experiences of supporting persons with IDD in the criminal justice system. Finally, the literature in the scoping review focused on the criminal justice system and did not include studies conducted in forensic services. Persons with IDD may be diverted from court proceedings to the forensic system due to questions of fitness to stand trial, competency, or criminal responsibility [42]. Furthermore, in jurisdictions like the UK, persons with IDD may be referred to community-based forensic intellectual disability services rather than incarcerated [42]. A future scoping review that includes forensic programs and services may provide a more complete picture of support and accommodations for persons with IDD involved in the criminal justice system.

Conclusion

This knowledge synthesis examined the interventions for persons with IDD at multiple stages in the criminal justice system. Results indicated that most of the peer-reviewed literature regarding these interventions focused on screening and intervention in earlier phases (e.g., police contact and court proceedings) and aimed to divert persons with IDD to more appropriate services and opportunities. Fewer interventions were found later in the criminal justice system. Intervention in later stages (e.g., correctional facilities and probation) of the criminal justice system is also important, given that it may influence future justice involvement and successful community re-entry. While the studies included in this scoping review indicate that a good effort is being made to ensure that persons with IDD are accommodated in the criminal justice system, more research is required to align efforts with the articles in the CRPD.