A criminal defense lawyer is a lawyer (mostly barristers) specializing in the defense of individuals and companies charged with criminal activity. Some criminal defense lawyers are privately retained, while others are employed by the various jurisdictions with criminal courts for appointment to represent indigent persons; the latter are generally called public defenders. The terminology is imprecise because each jurisdiction may have different practices with various levels of input from state and federal law or consent decrees. Some jurisdictions use a rotating system of appointments, with judges appointing a private practice attorney or firm for each case. United States 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. Often an attorney will specialize in a niche within criminal defense, such as drug defense or DUI defense. They could work for the local, state, or federal government or they could work for private law firms. The defense lawyers could also have their own practice and handle multiple criminal cases. An arrest simply means a police officer, federal agent, or judge believes probable cause exists that a person committed a crime. Since an arrest is usually made by law enforcement, the arrest often is for a criminal charge that has not been levied or verified by an attorney or judge. Criminal defense lawyers also deal with the substantive issues of the crimes with which their 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. The accused 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 charges by the prosecutor. Criminal defense lawyers in the United States who are employed by governmental entities such as counties, state governments, and the federal government are often referred to as public defenders or court-appointed attorneys. A considerable aspect of this work requires the US criminal defense lawyer to have a clear understanding of the United States Constitution. Specifically, the Fourth Amendment against unlawful searches and seizures. The Fifth prescribes a defendant's right to remain silent. The Sixth relates to a defendant's rights at trial. It guarantees a defendant the opportunity to confront and cross-examine witnesses, in