Matt Tonkin
Associate Professor of Criminology & Director of Research for the School
The majority of crime is committed by a minority of prolific serial offenders, with just 9% of offenders responsible for over half of crime committed in the UK. These prolific serial offenders impose significant human and financial costs on society, costing the UK economy an estimated £18.1 billion per year and leaving victims with significant physical and emotional injuries.
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Policing and criminal justice responses are, however, struggling to tackle the problem posed by prolific serial offenders:
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- 40% of adults with 11+ previous convictions reoffend within one year of their sentence ending.
- 40% of police investigations are closed without a suspect being identified.
- 94% of crimes reported to the police do not result in a charge or summons.
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If the public are to be better protected from harm, it is vital that more effective methods for catching and convicting prolific serial offenders are developed.
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Tackling serial offending relies on being able to identify crime series. This is called crime linkage – the decision that two or more crimes are the work of the same individual. Many approaches to crime linkage exist, but police often need to rely on offender crime scene behaviour to link crimes due to an absence of DNA at crime scenes. This process, called behavioural crime linkage, involves identifying the distinctive behavioural patterns that a serial offender repeats from one crime to the next. The identification of such patterns can be used to infer that two or more crimes are the work of the same offender or the same offending group.
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Successful behavioural crime linkage allows the evidence collected across multiple crime scenes to be collated, which can enhance the quantity and quality of evidence available to catch and convict serial offenders. Furthermore, linking crimes allows for multiple investigative teams to be combined, creating a more streamlined, cost-effective approach to crime investigation. If done correctly, behavioural crime linkage is, therefore, essential in the fight to tackle serial offending and to protect the public from the disproportionate harm these individuals inflict on society.
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Given the potential benefits of behavioural crime linkage to police investigations, criminal prosecutions and wider society, it is unsurprising that behavioural crime linkage is regularly practiced by crime and intelligence analysts and that units have been established around the world to support this specialised form of analysis. The Serious Crime Analysis Section (SCAS) is one such unit, established to support the identification of serial murderers and rapists across the UK.
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Police analysts and specialist units are, however, faced with considerable challenges when conducting behavioural crime linkage.
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The first challenge is volume – there are millions of crimes committed every year, making finding linked crimes akin to searching for two matching needles in a haystack.
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The second challenge is limited human resource – cuts to police funding over the last 15 years have significantly reduced the number of analytical staff available to conduct behavioural crime linkage.
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The third challenge is low technological capacity – while some analysts have access to automated systems to search for linked offences, these systems are rarely based on good quality evidence/research and they restrict how analysts would ideally like to conduct their analysis. Furthermore, many analysts simply don’t have access to automated systems, so are left to search for links manually amongst thousands of crime records.
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The fourth challenge is a chronic lack of knowledge, training and understanding regarding behavioural crime linkage – specialist units like SCAS are a notable exception, but policing generally is not equipped with an understanding of what crime linkage is, when and how it can benefit police investigations/prosecutions, nor what is required in terms of staff training, data collection and methods of working to deliver effective behavioural crime linkage.
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Together, these challenges mean missed opportunities to identify, detect and prosecute prolific serial offenders, resulting in continued harm being inflicted on society.
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So…what can we do about this situation?
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Fortunately, more than 20 years of research evidence exists to support the use of behavioural crime linkage by police and law enforcement agencies. This research can (and is starting to) be used to address the challenges outlined above.
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This body of evidence spans multiple crime types, from violent and sexual offences to property-oriented crimes, such as arson, robbery, burglary, and vehicle crime. The research is international in nature, with evidence to support behavioural crime linkage demonstrated in a wide range of countries, including the UK, mainland Europe, South Africa, US, Canada, Japan, Australia, and New Zealand.
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This research has demonstrated that serial offenders display sufficiently consistent and distinctive patterns of offending behaviour to support reliable and accurate crime linkage. Moreover, this research has developed and tested statistical algorithms that can automatically compare millions of offences in terms of their geographical, temporal and crime scene behaviour. These algorithms demonstrate high levels of accuracy when predicting whether crimes are linked or not linked. In ongoing collaborative research between the National Crime Agency, University of Birmingham, University of Leicester, and Imperial College London, these algorithms are currently being used to build computer software that will support human analysts to more effectively identify linked sexual offences committed across the UK.
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These developments are very exciting, but they are just the first steps in translating the wealth of academic knowledge on crime linkage into usable practical tools that can enhance the ability of law enforcement to conduct behavioural crime linkage. There will be many challenges – academic, technical, ethical/moral – but, with continued close collaboration between academia, law enforcement practitioners and policy-makers, I am confident that these challenges can be overcome to the benefit of society.
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