Behavioral Sciences of Terrorism and Political Aggression

Published by Taylor & Francis (Routledge)
Print ISSN: 1943-4472
Publications
Recent work on terrorism has identified a number of individual and group level factors that might contribute to terrorism anxiety and its implication for behaviour and cognition. However, few studies have tried to combine these factors into a coherent model. In this study we examined psychological responses to terrorism threats in the immediate aftermath of the London bombings in July 2005. Four-hundred and twenty-nine general public participants completed an inventory assessing terrorism anxiety, perceived likelihood of further attacks and their behavioural and cognitive consequences. Age, sex, normative expectations, values and personal control all predicted anxiety or perceived likelihood of attack. Anxiety was a significant predictor of negative coping, workplace distraction and increased interpersonal contacts. Implications of these findings are discussed in the light of continuing terrorist threats.
 
Stele perspective from below, photograph by Steven Brown.
In an era marked by the apparent saturation of terror and the ubiquitous mediation of all‐things‐past, the value of and the prospects for the remembering of terrorist attacks appear caught up in the velocity of the immediate circulation of media data and in the cyclical iterations of news images. Rather than these processes affecting a reduction or obliteration of memory, we discern how an interplay of individual and cultural frameworks is used for making sense of violent events in this environment through preliminary analysis of empirical work exploring the mediation and the commemoration of the 2005 London Bombings. We achieve this through cross‐fertilizing psychological and media and cultural studies approaches via the concept of ‘schema’ to show how remembering is dynamically configured through socio‐cultural practices and shifting media logics. In this way, we advocate a holistic approach to a ‘new memory ecology’, drawing upon the emergent field of ‘memory studies’.
 
This paper aims to discuss the application of crisis negotiation to individuals with a number of challenging traits, characteristics and behaviors, extending its application to terrorism. Such crisis situations include roof‐top protests and barricades, and any context that may include the need to re‐direct individuals in crisis, including terrorist activities such as hostage‐taking. This paper will review the history of crisis negotiation and consider different approaches to its management. It will then discuss the relationship‐building model of crisis negotiation of the Behavioral Influence Stairway Model. This is an updated variation of the Behavioral Change Stairway Model, which was first used in the wider community, and further applied here to traits and behaviors which may potentially be found in terrorist perpetrators. The application of this model to individuals who present with such traits and behaviors will be discussed, along with approaches to enhance and maximize negotiation processes with such individuals. This paper presents applications of the model and approaches to negotiation in terrorist situations.
 
The present article uses terror management theory (TMT) to explore the psychological, social and cultural forces that lead diverse groups and individuals to endorse, promote and enact violence against innocent individuals. From this perspective, it is the psychological function of religious, ideological, national or ethnic ties that is crucial for understanding how they can lead to hatred and violence. TMT provides an empirically based theoretically driven explanation of how ideological, nationalistic and religious values combine with historical events and concrete grievances to make terrorist violence appealing to those facing individual or group suffering. Research is presented which suggests that many of the same psychological forces that lead terrorists to their violent actions also lead to counter-terrorist policies that create massive collateral damage. This collateral damage appears to further escalate the cycle of violence and may aid the targets of those attacks in recruiting people for the terrorist cause. After examining the issues that inspire such violence, research is presented that suggests possible avenues to decrease support for actions that prolong inter-group conflicts.
 
This study investigated gaps in existing knowledge on justice, desire for revenge, and associated factors in disaster research through data collected nearly three years post disaster on justice and revenge from survivors of the September 11, 2001 (9/11) attacks. A volunteer sample of 379 employees of eight affected businesses completed interviews and self-report questionnaires. Individual ratings on satisfaction with justice and desire for revenge were compared with demographic characteristics, disaster-related experience, posttraumatic stress disorder (PTSD), disaster-related distress, anger, and concerns about danger and safety. High levels of desire for revenge and relatively low levels of satisfaction with accountability for perpetrators of the 9/11 attacks were endorsed. Most of the associations between the justice scores and the revenge score with the disaster response variables were directionally consistent. Dissatisfaction with perpetrator accountability was associated with greater desire for revenge. Both of these variables were associated with greater concerns about danger and endorsement of security regulations at the expense of personal freedoms.
 
Few researchers have analyzed post-9/11 alterations in the opinions or discourse of the legal community, despite this community's influence on public opinion and legal policy. In fact, to date, no source of data exists capturing the opinions of this community across the post-9/11 period. However, their writings in law review articles provide one source of longitudinal data regarding the issues and concerns that were salient to this influential community during the years of the post-9/11 era. A content analysis of law review articles is performed to examine meaningful shifts in the expert discourse related to civil liberties issues pre- and post-9/11 and across the post-9/11 period. The analysis – the first of its kind – demonstrates significant alterations over the post-9/11 period, including greatly intensified efforts at providing policy leadership. The analysis also reveals the year 2006 as a key turning point in legal scholarship, after which these articles adopted a highly aggressive, confrontational, and non-deferential tone. These findings are important because they inform scholarly debates regarding the role of elites in maintaining expansive civil liberties protections following terrorist attacks.
 
Majority respect for the political rights of minorities is an important value undergirding peace and political stability in societies. This study examines whether intolerance for minority political rights affects the likelihood that an individual has engaged in violent activities for political causes. Using public opinion data from 11 Arab countries, the study finds that Muslim residents who interpret Islam to mandate inferior political rights to their non-Muslims compatriots are more likely to have engaged in political violence in the past three years. Moreover, the effect of attitudes toward non-Muslim political rights on engagement in political violence is unaffected by subject support for Islamic government/rule, attitudes about democracy and Islamic government, interpretation of Shari’a and general intolerance of or bigotry against non-Muslims.
 
The main objective of this work is to analyse the mechanisms through which the attacks occurring on March 11th 2004 in Madrid could have influenced citizen’s vote decisions and hence the results of the legislative elections held three days later in Spain. It is argued that the most probable hypothesis is that the attacks influenced the voting decisions of citizens through a combination of several mechanisms: (1) the indignation caused by the belief that the government had violated a series of moral norms when trying to manipulate information to obtain an electoral benefit and (2) the anger and indignation that arose from attributing the political responsibility for the attacks to the government due to its support of the USA during the Iraq War.
 
We applied the path to intended violence (PTIV) [Calhoun, F. S., & Weston, S. W. (2003). Contemporary threat management: A practical guide for identifying, assessing, and managing individuals of violent intent. Specialized Training Services] model and the Terrorist Radicalization Assessment Protocol (TRAP-18; [Meloy, J. R. (2017 Meloy, J. R. (2017). The TRAP-18 manual version 1.0. Washington, DC: Global Institute of Forensic Research. [Google Scholar]). The TRAP-18 manual version 1.0. Washington, DC: Global Institute of Forensic Research]) to study the case of a lone-actor jihadist who carried out a fatal shooting at a joint Army-Navy recruiting center in Little Rock, Arkansas, on 1 June 2009. The PTIV model examines incidents using six progressive stages: grievance; violent ideation; researching and planning; preparation; probing and breaching; and attack [Calhoun, F. S., & Weston, S. W. (2003). Contemporary threat management: A practical guide for identifying, assessing, and managing individuals of violent intent. Specialized Training Services]. The TRAP-18 is a structured professional judgment tool and comprises 18 behavior-based warning signs for terror incidents. The findings from the retroactive application of the TRAP-18, in this case, show that in the week before the attack, the perpetrator exhibited 5 of the 8 proximal warning behaviors and 5 of the 10 distal warning behaviors. The retroactive application of the TRAP-18 and PTIV to cases of targeted violence assists with identifying a timeline of behaviors, which in turn provides insight into the pathway to violence and warning signs that someone may be a threat of violence.
 
Over the last 10 years, the concept of cumulative extremism (CE) has gained currency amongst both academics and policy-makers. Despite this, there is a dearth of empirical research into the idea. Furthermore, the extant literature – which has focused primarily on conflicts between social movements and groups in England – has not drawn firm conclusions into how and why processes of CE might develop. This paper will address this gap in the literature by examining the Troubles in Northern Ireland from its onset in the 1960s through to its peak as a lethal M/CM contest in 1972. In so doing, it aims to both improve the understanding of CE as well suggesting policy measures which might be employed to interrupt the escalation of movement–countermovement conflicts.
 
When states face international terrorism, their response almost automatically lies in the area of foreign policy. As such, actors in foreign policy making play a key, yet understudied role in this process. In this paper, I will therefore analyse West German foreign policy responses to Palestinian terrorism in the 1970s, which evolved from technical to diplomatic measures. The focus will be on the role of diplomats, not least on their sustained and expanding efforts to negotiate with representatives of violent Palestinian organisations after terror attacks affecting West Germany. This paper thereby shows the potential of a more actor-focused counterterrorism research agenda. Moreover, from a methodological standpoint it also illustrates how archival material can help to uncover the internal dynamics and complexities of governmental decision-making when it comes to counterterrorism.
 
This article examines the most rebellious movement in Danish post-war history – the leftist squatter movement in Copenhagen, 1981–2011 – thus recommending itself as a relevant case for the understanding of radicalization. The article's study of these squatters builds on the contentious politics approach and protest event analysis of 790 squatter actions. Based on this, the article discusses the causal status of “extreme ideas” and other inner factors compared to contextual factors related to the national and international political environment. It concludes that “ideas” have very limited explanatory value, whereas a specific political context of threats, opportunity, and interaction explains the radicalization and de-radicalization of the Copenhagen squatter movement with striking clarity.
 
Scholars and policymakers often make noticeable distinctions between acts of terrorism and mass shooting incidents. In order to assess if these distinctions are generally accurate, we identity four key criteria from standard international and domestic definitions of terrorism. The criteria include: a political, religious, ideological, or social motivation; intent to reach a larger audience; the motivation not involving personal monetary gain; and the manifestation of an ‘enemy/other’. We analyze 105 mass shooting events in the United States from 1982 through October 2018 to assess whether they meet these criteria and find that 41 (39%) incidents meet all four criteria and another 45 (43%) incidents meet three of the criteria to be classified as acts of terrorism. Thus, we contend that mass shooting incidents fit the standard definitions of terrorism to a greater degree than is often reported by government officials, academics, and media outlets. We contend that researchers must be more persistent in investigating the motivations behind mass shooting events in order to accurately label and counter them.
 
Despite the exponential growth in research on domestic counterterrorism over the past decade, relatively little is known about the actual effectiveness of specific counterterrorism policies in disrupting targeted terrorist networks. Using an original data set of network ties among British Islamists in the UK between 1999 and 2008, this study employs dynamic network analysis to assess the impact of the changes in UK counterterrorism policy on the network of radical Islamists operating in the UK. This research has significance for current and future domestic counterterrorism policy in the UK and other countries with populations at risk of violent radicalization.
 
This article introduces the Terrorist Attack Complexity Index, a framework to measure the complexity of terrorist attacks. This measurement takes place on the basis of 16 characteristics of terrorist attacks. The framework is applied to jihadist terrorist attacks in Europe during the period 2004–2011 to find perpetrator characteristics that are related to attacks with a high degree of complexity. The findings suggest that complex attacks are more likely to be carried out by perpetrators, who have gained expertise by visiting training camps outside Europe or participated in actual jihad, worked in large groups, and are acting on instructions from other terrorist groups. Simple attacks are generally carried out by perpetrators who have none of these characteristics.
 
This study conducts a Social Network Analysis on the neojihadist cell uncovered in Sydney in 2005. Detailed material is compiled and analysed to reveal a 10-man operational cell of Australian residents with an identifiable leadership, core and periphery. Although the cell was home-grown in origin, the group's genesis is traced to several members' interactions with international terrorist networks which previously operated in Australia. Indeed, the cell was far from an isolated entity, with a peripheral network of eight individuals identified as assisting in the group's formation and activities. A separate Social Network Analysis also demonstrated that the cell was interacting with a simultaneously developing neojihadist network in Melbourne. Upon analysing these connections it was revealed that these communications influenced both the ideological direction of the Sydney cell and provided the group with operational support.
 
The year 2017 had the deadliest incidents of gun violence ever in U.S. history; defined in our study as incidents with 4 or more persons killed or injured: 384 shootings with 466 people killed and 1,912 injured (Gun Violence Archive, 2017. Our study focused on the role of mental illness and other possible causes of gun violence by analyzing a minimum of three media reports and online documents related to each incident in 2017. Results showed that (a) information about the shooter(s) is available in only 157 (40.9%) out of 384 cases; (b) mental illness was mentioned as a cause in only 17 (10.8%) of the cases in which information was available; (c) subclinical or mental health issues such as relational stress, revenge, job stress, substance use, and trauma were mentioned much more often than mental illness; and (d) there are different types of gun violence. Based on these findings, future research should look at the complex interaction of perpetrator, situation, and victim variables, as well as socio-demographic and psychosocial/mental health variables that may clarify the role of mental illness in the different kinds of gun violence, one of which is mass shootings. Mental illness was not a significant contributing factor in this study’s gun violence cases.
 
There is a large discrepancy between the violent online rhetoric and offline behaviour of many extremists. Despite expressing militant views and support for violence, most individual extremists and many far-right groups do not engage in terrorism. Explaining this gap between discourse and action, researchers conclude that violent online rhetoric often serves several psychological purposes for individuals and groups, including playing an important role in building a collective identity. Scholars also conclude that groups sometimes strategize that terrorist attacks would be counter-productive to more important goals, or that internal struggles or disillusionment act as ‘brakes’ on the path to extremist violence. This study contributes to this research through an examination of New Zealand’s main white nationalist group, Action Zealandia. The study is based on 18 months of online and offline participation in the group by one author. We find that violent online rhetoric meets the nationalist needs of most members and the group’s leaders see violence as counterproductive. We also contend that face-to-face encounters between members temper the process of radicalization.
 
The Society for Terrorism Research and the Coloquios Internacionales sobre Cerebro y Agresión (CICA) held their 6th annual international conference on terrorism and aggression in Burgos, Bulgaria 8 September through 11 September 2012. Hosted by Sofia University, the conference focused on the dynamics of terrorism; new security challenges; the psychological and social impact of aggression, violence, and terrorism; social and gender implications of violence; dispute resolution; and practical approaches to prevention and intervention. More than 80 participants came from 23 countries to present their research, share their ideas, and collaborate in their efforts to bring resolution to the global problems posed by terrorism and violence.
 
This paper analyses the impact of a series of mass shootings committed in 2018–2019 by right-wing extremists on 8chan/pol, a prominent far-right online forum. Using computational methods, it offers a detailed examination of how attacks trigger shifts in both forum activity and content. We find that while each shooting is discussed by forum participants, their respective impact varies considerably. We highlight, in particular, a ‘Tarrant effect’: the considerable effect Brenton Tarrant’s attack of two mosques in Christchurch, New Zealand, had on the forum. Considering the rise in far-right terrorism and the growing and diversifying online far-right ecosystem, such interactive offline-online effects warrant the attention of scholars and security professionals.
 
Anti-abortion extremism is difficult both to quantify and qualify due to its diverse nature and poor data availability. This article presents a relationship between all types of anti-abortion protest and relevant factors studied in previous research. In support of the “safety valve”, “general strain” and “substitution”, or “functional displacement” theories, this article concludes that anti-abortion protest rose and fell along a continuum of extremism in response to political frustrations. This article offers examples of how the matter can be more thoroughly and systematically analyzed.
 
Narrative has recently garnered in much attention in the study of terrorism but remains poorly understood. This paper offers some initial steps towards translating the promise of narrative approaches into a set of steps for systematically analysing and understanding terrorists’ own accounts of their engagement with extremism and militancy. This approach rests on the assumption that terrorist authored accounts are more than post-hoc rhetorical exercises that aim to persuade others, or even the authors themselves, of the righteousness of their political cause or otherwise mitigate their responsibility for their involvement in violence. In particular, I advance a framework for methodically applying narrative approaches to terrorist authored texts, in particular, autobiographies. In doing so, I will demonstrate how this approach can help better comprehend how individuals involved in militancy understand the world, draw upon existing narrative resources and give meaning to their actions.
 
Previous research shows that acculturation challenges predict immigrants’ support for terrorism. Here, we acknowledge the central role of mass media use in the acculturation process. We investigate whether immigrants who infrequently use ethnic and host country media, a possible indicator or driver of marginalisation, report higher sympathy with terrorism than frequent media users. We further examine if those who prefer ethnic over host country media, which might reflect or facilitate disengagement from the host society, support terrorism more strongly. To address these research questions, we conducted secondary analyses of a public opinion poll of Muslim immigrants resident in the United Kingdom (N = 880). Focusing on immigrants’ use of ethnic and host country television channels, latent class analysis identified four groups: Frequent and Infrequent Media Users as well as Ethnic and Host Country Media Users. Overall sympathy with terrorism was low. Contesting our hypothesis, Frequent Media Users supported terrorist action more than Infrequent Media Users. Ethnic Media Users also expressed higher sympathy with terrorism than Host Country Media Users. Findings emphasise the dynamic interplay between media use and acculturation challenges; they further suggest strategies to reduce immigrants’ support for terrorism.
 
The distinctive nature and complexity of judging terrorist acts include collective, political, and social dimensions that should be taken into account. The present study examines how participants from the general public in France perceived the perpetrator of a terrorist act, varying in ethnicity (North African vs. French) and gender (male vs. female). Based on a scenario describing an attempted terrorist attack and the offender, participants indicated their perceptions about the act and the perpetrator (content of stereotypes, emotions, behavioral responses, degree of agreement, perceived threat, severity of the sentence). The participants’ ideological orientation was also measured. Results revealed that participants judged the North African man more harshly than the other profiles. The impact of stereotypes on their judgments and perceptions was only partially observed. But generally, the presentation of a North African vs. a French offender seems to activate the effect of participants’ social dominance preferences on their judgments. In this study, the perception of individuals committing terrorist acts appears complex, and the results are discussed in relation to the existing literature.
 
Dataset Comparison of Muslim Convert Percentages..
Parallel mediation and covariation hypotheses.
Convert vs. non-convert sample demographics.
Muslim converts are overrepresented in Islamist terrorism compared to non-convert Muslims – Why? To explore possible explanations, we probed aspects of radicalism and Islamic religiousness within relevant populations. Specifically, we surveyed 356 American Muslim adults, of which 177 were self-identified converts, with the Activism and Radicalism Intention Scale (ARIS: Moskalenko & McCauley [2009]. Measuring political mobilization: The distinction between activism and radicalism. Terrorism and Political Violence, 21(2), 239–260. https://doi.org/10.1080/09546550902765508) and the Psychological Measure of Islamic Religiousness (PMIR: Abu Raiya et al. [2008]. A psychological measure of Islamic religiousness: Development and evidence for reliability and validity. The International Journal for the Psychology of Religion, 18(4), 291–315. https://doi.org/10.1080/10508610802229270). We used the ARIS because terrorism is rare, but radicalism and activism are more common. Activism and radicalism engagement may correlate with terrorism engagement, though they are neither necessary nor sufficient antecedents. We found that converts, compared to non-converts, demonstrated higher intent to engage in activism and radicalism on the ARIS, and that they experienced greater Religious Struggle and lower Fear of Punishing Allah Reappraisal (PAR) on the PMIR. We also found that both of these PMIR factors partially mediated the relationships between conversion and activism/radicalism. We propose that this is because converts feel a pressure to prove their faith, especially when they believe Allah punishes unfaithfulness. We discuss these findings in light of current psychology and political mobilization literature and then offer suggestions for future research on the relationships between conversion, radicalism, and religious experiences.
 
Many members of minority groups clash violently with state agents. The case of the Israeli West-Bank Settlers’ Right-Wing Activists is particularly paradoxical. Unlike disempowered groups whose ability to bring about change is limited – the Settlers constitute a powerful sociopolitical force, and the security forces with which Settler Right-Wing Activists clash, also protect them in territories to which they claim sovereignty. Based on 20 semi-structured interviews, this article provides explanations Settler Right-Wing Activists give to violent clashes in which they were involved. The findings present two non-mutually exclusive possibilities: (1) violence is perceived as an acceptable sociopolitical change strategy. Interviewees agree to risk themselves as individuals (but not to risk their group) in exchange for potential benefits such as preventing settlement evacuation; (2) Violence indicates declining mainly four out of six different components of perceived state legitimacy: trust, distributive justice, procedural justice, and legality, but primarily not identification and effectiveness.
 
Temporal aspects of pre-attack behaviors. 
This article explores the link between radicalization patterns and modes of attack planning and preparation among lone-actor terrorists. Building on theorized patterns of lone-actor radicalization, we discuss and compare their modes of pre-attack behavior, including target and weapon choice, observance of operational security measures, likeliness of engaging in leakage behavior, and the overall amount of time devoted to these activities. This exploratory study builds upon a dataset of thirty-three lone-actor terrorist cases in North-America and Europe between 1986 and 2015. The analysis suggests that specific patterns of radicalization are linked to systematic differences in modes of attack planning and preparation. The results provide insights into the heterogeneity of terrorist involvement and tentatively suggest the potential importance for law-enforcement agencies in using case-specific knowledge on radicalization patterns to inform forecasts of likely pre-attack behaviors.
 
Leakage is one of the eight warning behaviors referred to in the violence risk and threat assessment literature. Previous research has highlighted the relevance and prevalence of leakage in lone-actor terrorists; however, a more detailed understanding of this phenomenon is lacking. This study sets out to expand our knowledge of this behavior by conducting an exploratory analysis using court records relating to IS-inspired lone-actor terrorism cases in the United States. The general patterns in leakage warning behavior were analyzed, and different types of leakage were examined with regard to from whom they were leaked, how they were leaked, their presence online, and whether or not they occurred before certain types of attacks more than others. It was found that leakage in the form of support tended to be leaked most frequently to members of the public, via written text and online, whilst the leakage of intent and specifics appeared to be more regularly leaked to co-conspirators and through verbal communication that avoided the online world. Significant relationships were also found between leakage, FBI interaction and attack initiation, but no significant relationship was found between leakage and mental health. The implications of these findings are discussed.
 
Attempts to profile behavioural factors of lone actor terrorists have resulted in inconclusive data arguing that the wide range of individual characteristics makes it difficult to categorise lone actor terrorists. Instead, research should investigate the methods used by lone actor terrorists such as the release of a manifesto. The present study used a mixed methods approach to analyse manifestos created by lone actor terrorists (n = 19). Smallest Space Analysis of the language variables within lone actor terrorist manifestos was used to identify three language typologies: Instigator, Planner, and Conspiracy typologies. Findings indicate that 89% of the case studies reviewed were able to be categorised into a typology based on the language used. Further analysis identified key language variables that can be found within the manifestos in each typology combined with behavioural factors to develop a language profile of each typology. Applications of the research are also discussed as well as limitations and future areas of research development.
 
Theoretical framework.
Comparison of selected cases to sample: paersonal characteristics.
Comparison of selected cases to sample: Attack characteristics.
Mechanisms and empirical indicators
Continued.
How does the internet affect the radicalisation of extreme-right lone actor terrorists? In the absence of an established theoretical model, this article identifies six mechanisms seen as particularly relevant for explaining online radicalisation. Having first reviewed a larger set of relevant lone actor terrorists, the study traces these mechanisms in three selected cases where the internet was reportedly used extensively during radicalisation. The findings show that the internet primarily facilitated radicalisation through information provision, as well as amplifying group polarisation and legitimising extreme ideology and violence through echoing. In all three cases, radicalisation was also affected considerably by offline push-factors that through their presence made extreme online messages more impactful. The results challenge the view that offline interaction is necessary for radicalisation to occur but also the view that online influence itself is sufficient.
 
Terrorism is often held to be “violence as communication”. However, terrorism studies has had very little to say about how violence as such is specifically represented by insurgent “extremist” or transgressive political actors. Informed by social movement theories of framing and the literature on virtualization, this paper sets out to offer a preliminary typology of representations of violence by such groups, and the ways in which subcultural engagement with mediated representations of violence may represent a missing dimension in our understanding of “violent extremism” or “violent radicalization”.
 
Addressing violent extremism could potentially benefit from new initiatives that extend beyond criminal justice and are a part of public health policy and practice. This claim is based on knowledge from prior countering violent extremism (CVE) research and on immersion with communities, practitioners, and policymakers. This knowledge indicates that to date law enforcement-centered initiatives have not generated targeted evidence-based prevention or intervention initiatives, and they have had the unintended consequence of provoking community resistance. The Center for Disease Control’s Ten Essential Public Health Services is proposed as a new conceptual framework for a public health approach to addressing violent extremism which aims for policy and practice shifts. The public health approach offers opportunities for multi-purpose programming, avoiding stigma, and leveraging existing public health resources. Such shifts are illustrated by discussing the CVE program being further developed in Los Angeles, California, based in part upon the public health model.
 
Top-cited authors
Kate Barrelle
John G Horgan
  • Georgia State University
Bart Willem Schuurman
  • Leiden University
Michael Williams
  • The Science of P/CVE LLC
Edwin Bakker
  • Politieacademie