Civil or military police, or government agents, may entice or lure individuals or groups into breaking the law. This may be done to apprehend known criminals by having an undercover officer party to the incriminating act and therefore able to testify concerning it, if in fact, the individual concerned is not caught 'red-handed' in the act itself. Trapping individuals in this manner may also be used to incriminate and convict enemies of the state and political dissenters, by leading them to break laws concerning the national interest or censorship. Entrapment is illegal in many countries, in particular because it may be abused; it may cause an individual to commit a crime in order to punish him, when in fact the crime would not otherwise have been committed at all.
Where individuals cannot be tricked or entrapped into breaking the law, and are innocent of wrongdoing, law enforcement agents may introduce or plant evidence of law-breaking in the individuals residence, office, automobile, or other property, or in clothing; or they may falsely testify that they found incriminating evidence in the individual's possession. Where the nature of the act does not require physical evidence, agents may conspire to incriminate individuals by giving false witness and perjuring themselves, or by using paid or black-mailed individuals in their place to testify against the innocent. These acts are criminal under all legal systems but occur nevertheless.