The aim of the Digital Police Officer project (DPO) is to identify cybercriminals based on their writing style. When a criminal underground forum is closed down, cybercriminals move to another one to further their illicit business. These users do not necessarily return with the same uername. We are producing a demo that can still identify such cybercriminals. We look at the way they communicate, analysing the characteristics of forum users (i.e. based on their vocabulary and grammar) to build a linguistic fingerprin