Authorities are bound to rules. When solving crime not all are means allowed. Many regulations are written in laws. Many other regulations can be found in court decisions. The so called Tallon criterion (1979) is one of these regulations not to be found in the law itsself.
The case is about under cover agents who infiltrate in international drugs trading.
There is a fine line between what is allowed and what is not allowed. In short ‘people may not be ‘encouraged’ to act differently than they already intended to act before’. The police may not provoke people into crime.
However in 2008, the Supreme Court in The Netherlands decided the usage of bikes to catch thieves is allowed.