Whilst the law and procedure on special investigative techniques are specific to each jurisdiction, there are some fundamental principles that underpin the use of the techniques and these are common to all countries.
Special investigative techniques – covert surveillance of one form or another – are vital tools in the pursuit of terrorists. The issue with them is that they tend to undermine the human rights of those they are used to investigate or, worse still, of innocent people who encounter the subject of the investigation in their everyday lives. It’s usually the right to privacy which is undermined most readily by the techniques. That’s why most countries have special laws and procedures designed to ensure that the techniques are not abused.
The four fundamental principles that underpin the use of these techniques are called the human rights principles. They are: Proportionality, Legality, Accountability and Necessity (so we can use the nemonic ‘PLAN’ to remember them).
Proportionality – is the objective proportional to the technique?
Legality – is the use of the technique legal in the circumstances?
Accountability – is the use of the technique correctly authorised and recorded?
Necessity – is it necessary to use the technique in the circumstances, or could a less intrusive technique achieve the same objective?
All four principles must be adhered to.