The investigator, who is often a police officer, takes statements and collects evidence to be used in criminal prosecutions. Statements may be taken from victims of the crime, witnesses, or anyone who knows something about the alleged offence.

Once the investigator thinks they have enough evidence to charge someone with a criminal offence, they compile a brief with all the information they have about the crime. This includes witness statements and physical evidence like photographs and recordings. When it is ready, a brief of evidence is referred to the CDPP for assessment.

• Once a prosecution has started, the investigator becomes known as the informant or complainant.

 The CDPP does not investigate offences, it prosecutes crimes against Commonwealth law.