Arrest is the act of taking a person into the custody of the law and depriving the person of liberty. The term comes from the French word arreter, which means to stop. Any police officer may make arrests. Agents of the Federal Bureau of Investigation also have the power to make some types of arrests. Private citizens have the right to make an arrest if a serious crime is committed in their presence. People may be arrested after they are accused of murder, theft, or other criminal offenses. For some crimes, and under certain conditions, a police officer must obtain a court order called a warrant before making an arrest. But an officer does not need a warrant to arrest a person in the act of committing a crime. Ordinarily police may arrest anyone whom they reasonably believe to be guilty of a serious crime.