The methods that law enforcement agents traditionally use to identify dangerous individuals in public locations involve observation of behaviour and the use of knowledge gained in previous investigations. Officials may even institute random checks in particularly high risk situations. Customs officers will try to identify drug smugglers passing through an airport by using police information about delivery dates and bank transactions to determine when they should increase checks on luggage; security staff will be instructed to be alert for anyone who appears nervous, agitated or evasive.

The ability to observe and interpret behavioural indicators, no matter how subtle, has been at the core of police work for decades[i]. This skill guides the training of new police officers and is prized by security professionals. Financial transactions and travel patterns- the things that we buy and the places that we visit- can also constitute a form of behaviour. The computer systems used to monitor international travel and immigration can already be programmed to monitor travellers with criminal records, or who are en route to poorly governed or insecure states. Intelligent observation and interpretation of information acquired by borders authorities can also be useful in detecting criminal activity or intent. Even passports contain more information- both human-readable and digital- than ever before.

Profiling is a policing technique that attempts to predict whether or not an individual will behave in a criminal fashion based on his personal characteristics rather than his behaviour[ii]. Profiling need not be targeted against a particular person; it can be used to identify members of a class or group[iii]. One of the advantages of profiling is that it allows police to direct their attention and observational skills on to individuals thought to pose the greatest risk of breaking the law. The most sophisticated forms of profiling study an individual’s background and psychological characteristics. Simpler profiles focus on gender, age and race. For example, decades of behavioural studies indicate that women are less likely to commit impulsive, violent offences than men. A profile used to identify individuals who may attempt to start riots at sports events would therefore exclude women. Profiles guided by an individual’s race have proved controversial, as they may be based on an implicit assumption that racial background can determine behaviour[iv], suggesting a connection between an individual’s skin colour and her willingness to obey laws and social norms[v].

Investigations carried out in the wake of the 9/11 attacks confirmed that all of the hijackers were of Middle Eastern origin and appearance. Some had entered the US on student visas; others had been resident for extended periods of time. Once links between these individuals and al Qaeda were confirmed, it was quickly assumed that the majority of the organisation’s members were of a similar ethnic and racial background. A number of investigators reasoned that people from majority Muslim states and racial groups were more likely than other individuals to be members of al Qaeda[vi], due to the group’s integration of radical Islam and violent, insurrectionary politics. As the 9/11 hijackers had exploited flaws in airport security, investigators advocated increased security at airports and intensive and intrusive screening of passengers who were Middle Eastern or “Muslim” in appearance.

Although the law governing security screening at US airports changed little, screening staff employed by the TSA were given instructions based on profiling theory[vii] that led to large numbers of individuals from Arab and Muslim states being subjected to lengthier and more intimate searches[viii].

Supporters of profiling point out that seasoned security officers’ ability to identify dangerous individuals by their behaviour is all but useless within a busy airport. It is not possible for a handful of officers to focus sufficient attention on each of the millions of passengers that pass through Kennedy, LAX or Heathrow, nor is it possible to hire and train enough staff to close this gap. By eliminating the types of passenger thought least likely to be terrorists, the skills and insight of experienced officers can be employed more effectively.

It has also been pointed out that selecting individuals for intrusive searches on the basis of their skin colour is a policy that can be justified by the potential loss of life that would be caused by another terrorist hijacking. An opportunity to prevent thousands of deaths and extensive property destruction balances out the subtle distortions in attitude and the offence that racial profiling might cause. Moreover, the journalist Stuart Taylor[ix] has noted that forced removals of Middle Eastern individuals from aircraft following the 9/11 hijackings were not caused by entrenched racist attitudes, but by a lack of confidence in the security screening processes that airports were using. By reassuring flyers that their fellow passengers have been subjected to searches proportionate to the threat that someone sharing their characteristics might pose, there is less chance of airlines preventing individuals from flying on the basis of poorly informed and racist policies.

Contrary to the arguments used by profiling’s supporters, civil rights and anti-racism campaigners claim that the use of profiles causes screeners and investigators to pay more attention to individuals’ racial and ethnic characteristics than their behaviour. They point out that the distinction between physical appearance and behaviour can easily be blurred. Openly designating a particular group or class of individuals as being potentially dangerous may lead otherwise competent security staff to identify suspicious and threatening forms of behaviour more frequently than they would in other contexts. Selection biases of this type will also cause officers to overlook disturbing behaviour engaged in by individuals who do not fit the profile that they have been trained to recognise.

Finally, those opposed to profiling note that building close and open relationships with the communities that terrorists might belong to is at least as important as preventing them from reaching their targets or boarding aircraft. Terrorists pose a threat to their families and cultures, as well as their targets. Terrorist actions, based on distorted interpretations of a particular religion, may expose mainstream members of that religion to reprisals and prejudice. Indeed, terrorists may go out of their way to target members of their own community whom they perceive as holding heretical or unacceptably lax beliefs and views. Profile-led searches, no matter how nuanced, will inevitably lead to young Muslims and Arabs being equated with terrorists. If these individuals come to believe that law enforcement officials are overly keen to link them to terrorist acts, to investigate and arrest them, they are less likely to help voluntarily with police enquiries. Moreover, they are less likely to report dubious or unusual behaviour to the police. Many of the leads on terrorist activity that bodies such as the FBI follow up start out as nothing more than vague and petty concerns. Anti-profiling campaigners argue that targeted airport searches will undermine any possibility of creating an effective relationship between law enforcement agencies and Arab and Muslim communities.