Given the attacks in the winter of 2019-2020 in the UK, such concerns appear to be well founded. However, there is considerable debate over the actual level of threat posed by terrorist offenders on their release. The research on levels of terrorist recidivism is far from conclusive, and reliable data on the subject are scarce and complicated by a range of methodological issues.
However, recent analyses of the problem in Europe point towards a relatively low rate of recidivism amongst released terror offenders. A 2016 study of a Dutch rehabilitation programmme established a recidivism rate of roughly 4%. A more recent Belgian study assessed that, among 577 offenders, there were only 13 cases of recidivism, a lower rate of around 2.3%.
These figures are broadly consistent with Home Office statistics for England and Wales, which showed, between 2013 and 2019, only six terrorist offenders of a total of 196 were convicted for terror offences a second time. Such figures are contrasted favourably with recidivism rates for non-terrorist offenders, estimated to be around 45-55% in most Western countries. However, a direct comparison of the two rates is disingenuous; while the reconviction of non-terror offenders on any charge will lead to their inclusion in general recidivism statistics, terrorist offenders must commit further terror offences to be included in terrorist recidivism figures.
Recidivism vs reengagement
Furthermore, low rates of recidivism do not necessarily reflect low rates of reengagement in extremist activity. Reengagement refers to a return to terrorist activity having been disengaged, either by choice, or through incarceration. Despite reengaging and reoffending, neither Usman Khan nor Sudesh Amman would be counted in recidivism statistics, as both were killed because of their actions, which prevented them from being prosecuted.
Attempts to measure reengagement rates are plagued by many of the same including small sample sizes, varying methodological approaches, and often incomplete cross-national data.
However, it seems likely that reengagement rates are at least somewhat higher than recidivism rates, not least for the reason given above. Reengagement need not take the form of attack planning (released offenders may apply themselves to recruitment or fundraising activities, for example) and would therefore contribute indirectly to the level of threat. Nonetheless, the current volume of terrorist offenders imprisoned across Europe means that, even if only a small minority of those released in coming years reengaged, it would still constitute a significant additional operational burden for police and intelligence services. A bigger challenge is extremists who did not travel to the Middle East to engage and therefore have not been prosecuted.
Furthermore, attempting to discern whether terrorist offenders actually have disengaged from extremism remains a challenge, particularly given the weakness of monitoring and control in this space. Usman Khan had participated in two rehabilitation schemes whilst in prison and on parole, and was viewed as sufficiently benign as to be granted a day-pass to travel to London (travel restrictions were a condition of his parole).
In contrast, police harboured major concerns about Sudesh Amman on his release, and he was therefore placed under close armed surveillance, which ultimately limited the lethality of his attack.
An intractable problem
While recently introduced measures are intended to improve assessment of the threat posed by released terror offenders, it is improbable that these will be entirely foolproof. It is therefore likely that the police and intelligence services will continue to allocate considerable resources to monitoring even those released terror offenders not deemed to represent an immediate threat.
Given this, the government’s desire, reflected in the new tougher sentencing and release measures, to keep terrorist offenders in prison is entirely understandable. However, while longer sentences (and greater scrutiny of early releases) may keep potential recidivists away from the public for a time, most of the UK’s terror offenders are serving sentences of less than 20 years, with many jailed for under four years. Therefore, significant numbers of terror offenders will be released in the near term despite government action. Moreover, without greater success in rehabilitating convicted terrorists, such measures are unlikely to be that effective at reducing the threat of terrorism in the long term. The risk of recidivism or reengagement by those released will vary significantly depending on a range of factors, including age, sentence length, affiliation with terrorist groups, family life, engagement in deradicalisation programmes, and the stringency of monitoring and control measures.
However, even the most optimistic studies of recidivism suggest that a small minority will reengage with terrorism. The threat they pose will depend on the nature of their reengagement, and the response of the police and intelligence services. While some may eschew attack planning and engage in facilitating activities, with a lower probability of detection, others may follow the example of the London Bridge and Streatham High Street attackers. In this scenario, it is likely that these individuals would employ the same low-complexity tactics in order to minimise the chances of their intentions being detected and their plans thwarted. Such attacks require very little preparation and few resources; indeed, Sudesh Amman procured his weapon, a kitchen knife, by stealing it from a homeware store immediately before launching his attack.
Such low-sophistication attacks are virtually impossible to stop, while resource-intensive close surveillance operations will be restricted to only the highest risk cases. This means outcomes similar to that of the Streatham attack are far from certain. Without rapid police intervention, even rudimentary tactics can inflict significant loss of life, with resulting man hunts and subsequent investigations causing widespread disruption. Organisations should therefore plan and prepare for such eventuality even if, owing to the work of the police, intelligence, probationary and other government services, they will fortunately remain an infrequent occurrence.