Criminal cases are lawsuits by which the State prosecutes a person or organization for the violation of a penal law.
A penal law is that which identifies which acts or omissions are considered as crimes or offenses. There must thus be a specific provision in a Penal Code or Special Penal Law that defines and punishes the act or omission before one is considered to have committed a crime. Even if an act is socially or morally wrong, no criminal liability is incurred by a person or organization until that act is classified as a crime under law.
When one is being prosecuted for a crime, it is the State which is actually suing the offending party, and not the private injured party. This is because crimes are considered offensive to the peace and order of the country. The private injured party becomes a witness for the State.
In Thailand, prosecution for criminal law is the responsibility of several government organizations: the Royal Thai Police, Office of the Attorney General, the Courts of Justice, the Ministry of Justice and the Ministry of Interior.
Aggrieved parties commonly go to the Police to make a report of a criminal incident. The Police then proceeds to investigate the alleged crime and reports its findings before the Office of the Prosecutor. The Office of the Prosecutor, on the other hand, files the appropriate criminal case in Court.
The overwhelming number of criminal reports have resulted in delays in investigations and prosecution. As a solution to this, private citizens have been allowed to come to hire lawyers who will directly file the criminal case in courts, instead of taking the police reporting route. While this is a more expedient choice, the private party of course bears the consequence of bearing the costs of the private case filing.
Only judges decide criminal cases in Thailand. The jury system does not apply in this jurisdiction. As everywhere else, the court must find proof beyond reasonable doubt before it convicts an accused of the crime he is being tried of.