In the United States, criminal defense lawyers deal with the issues surrounding an arrest, a criminal investigation, criminal charges, sentencing, appeals and post-trial issues. An arrest simply means a police officer or judge believes probable cause exists that a person committed a crime. An arrest does not necessarily mean that a criminal charge has been claimed by attorney. Criminal defense lawyers also deal with the substantive issues of the crimes with which his or her clients are charged. Criminal defense lawyers may also help clients before charges have been filed by a prosecuting attorney. This is done when someone believes he or she is being investigated or is arrested. The person may hire a criminal defense lawyer to help with counsel and representation dealing with police or other investigators, perform his or her own investigation, and at times present exculpatory evidence that negates potential charge by the prosecutor. Criminal defense lawyers in the United States who are employed by governmental entities such as counties, state governments, and the federal governments are often referred to as public defenders or court-appointed attorneys. A considerable aspect of this work requires the criminal defense lawyer to have a clear understanding of the United States Constitution. Specifically, the Fourth Amendment protects against unlawful searches and seizures while the Fifth and Sixth Amendments govern the right to remain silent so one does not become a witness against himself. All of the Amendments to the United States Constitution are guaranteed to the criminal accused against the states via the Fourteenth Amendment. Thus, a criminal defense lawyer must understand each of these rights. Initial work on any criminal case involves review of the charges and the claimed facts, and analysis of constitutional violations, the prima facie burden of the prosecution, defenses, and affirmative defenses; as well as potential sentence and sentencing issues. Early stages of a criminal case may involve a grand jury or preliminary hearing to determine if there exists probable cause for the case to continue. A violation of the Fourth or Fifth Amendment, or other illegally obtained evidence could result in evidence being inadmissible at trial. Accordingly, a criminal defense lawyer often spends a considerable amount of time reviewing all documentation to determine if the case can be won on Constitutional Grounds due to illegal conduct by the government.