A criminal conviction results when a prosecutor proves in a court of law that a given individual violated the penal code or common law rules. Within each society, rules exist that — if violated — subject a person to criminal prosecution. In many societies, including the United States, those laws exist both in common law, or judge made rules, and in federal or state statutes passed by the legislatures.
The body of criminal law is designed to ensure widespread protection of all citizens. It makes illegal certain behaviors that are bad for public health or that violate the moral code of society as a whole. The violation of these criminal laws come with penalties.
A person who violates the body of criminal law enters into the criminal justice system. While the process differs slightly from country to country, usually the police will investigate a crime to determine who was responsible for the violation. In some cases, the police may directly observe a crime — such as seeing someone drive drunk — and no investigation will be required.
When there is sufficient proof of a person's guilt, an officer of the court — normally a prosecutor — will seek permission from the court to arrest the party. This is called an indictment. The party is then arrested and brought to court to enter a plea of either guilty or not guilty and to then stand trial for the crime.
During a criminal trial, the prosecutor presents evidence aimed at getting a criminal conviction on the accused party. This evidence is presented to a judge and a jury and then the judge or jury determines whether the accused criminal is guilty or innocent. Rules of evidence apply which limit the type of proof a prosecutor can introduce, and standards exist to determine exactly what the prosecutor must prove to get a criminal conviction. In the United States, for example, the prosecutor must prove that the accused defendant was guilty beyond a reasonable doubt for the jury to convict.
When a criminal conviction is handed down by the judge or jury, penalties follow. The penalties depend on the type of conviction and the seriousness of the crime. For a criminal conviction for a minor crime — called a misdemeanor in the United States — the penalties may involve a fine or community service. For a more serious conviction, such as murder, the penalties are much more severe and may even constitute death.