Final answer:
The initial determination of probable cause for an arrest made without a warrant is usually made by the police officer involved. This determination is later reviewed by a judge, guided by the legal standards set forth in the Fourth Amendment.
Step-by-step explanation:
For arrests made without a warrant, the initial determination that there might be probable cause will be made by a police officer. Probable cause is a legal standard for determining whether a search or seizure is constitutional or a crime has been committed; it is a lower threshold than the proof standard required at a criminal trial. When arrests are made without a warrant, particularly in cases of felony crimes where probable cause exists or when a law enforcement officer has witnessed a misdemeanor, the officer on the scene makes the probable cause assessment. Subsequently, the determination is typically reviewed by a judge, especially at a preliminary hearing. The Fourth Amendment lays the framework for this process, which is designed to prevent unreasonable searches and seizures and requires any warrant to be backed by an oath or affirmation particularly describing the place to be searched and the persons or things to be seized.