The criminal justice system refers to the court system, the prison and jail system, and the system within a society by which accused people are tried for crimes and punished. There are numerous components of this system, from the police who investigate crimes to the lawyers who prosecute cases and the judges who preside over the courts. Prison systems and parole officers are also part of the system.
In most developed countries, there is a body of criminal law. Criminal laws dictate what behaviors are forbidden and punishable by the state. Criminal law is distinct from civil law, which refers to duties that people have to each other that are enforced in private lawsuits. Violation of criminal law can result in prosecution and punishment by the state itself.
Most countries also have codes in place to protect accused criminals. Canada and the United Kingdom both protect the rights of the accused in their chartering documents, such as the English Bill of Rights. The United States protects accused people through the due process clause in the Fifth and Fourteenth amendments, the right to a trial by jury in the Sixth Amendment, and the right against self incrimination in the Fifth Amendment.
The criminal justice system thus must operate to enforce criminal laws and punish those who violate them, while also protecting the rights of the accused guaranteed by the fundamental laws of the state and country. Those who are in the system, from the police to the attorneys, act as officers of the court or officers of the state. They are expected to behave appropriately, fairly and justly when it comes to the rights of the accused.
When a person is accused of a crime, he moves through the criminal justice system according to the process determined by the authorities that established the system. This usually means he is questioned, and evidence is collected on the crime. An attorney for the state, often referred to as a prosecutor, thus determines whether there is enough evidence to request an arrest warrant be issued.
If an arrest warrant is issued, the accused enters the court phase. The exact process differs among countries, but generally during this phase of the criminal justice system, both the prosecution and the defense present evidence to convince a judge or jury that their version of events is correct.
If the person is found guilty in a trial, he continues to move through the criminal justice system. He is sentenced according to criminal laws, to either jail time or some other punishment. If he is sentenced to jail time, he remains in the justice system and serves his sentence in a federal or state prison or jail.