United States v. Watson
The case that established this principle is United States v. Watson (1976). The Supreme Court held that an arrest without a warrant, made by law enforcement officers in a public place, is valid if they have probable cause to believe that a crime has been committed.
Most juridictions allow arrest for a felony without a warrant as long as probable cause for the arrest can be articulated.
Without a warrant you must find reasonable grounds to arrest someone, whereas with a warrant your reason to arrest the suspect already exists. Without a warrant a Police Officer can arrest anyone without permission of a Magistrate as long as they follow the correct procedures so their arrest is lawful, which is unlike an arrest with a warrant where you must be granted the warrant to be able to arrest that person. Without a warrant, a Police Officer can mess the arrest up and make it an unlawful arrest but with a warrant it is very unlikely that they make it an unlawful arrest.
Probable cause is typically established when there is enough evidence to suggest that a crime has been committed or is about to be committed. This evidence can come from witness statements, physical evidence, surveillance, or other investigative techniques. Probable cause is required by law before a search or arrest can be conducted.
probable cause
A police officer must have probable cause in order to arrest someone. They can arrest a person if they see a crime taking place or if an arrest warrant has been issued.
judge
Probable cause or warrant
Probable cause or a warrant.
When he has probable cause to believe that the person he is arresting has committed, or is about to commit, a criminal offense.
In California an arrest for a misdemeanor can be made without a warrant IF the offense was committed in the presence of the officer/citizen making the arrest ( see penal code section 836 & 837. Arrests can also be made for a felony without a warrant IF a felony has in fact been committed and you have probable cause/reason to believe the person committed the felony.
Until he has sufficient probable cause to sustain a warrant for an arrest.
If they have probable cause to do so, yes. With probable cause, or an arrest warrant, law enforcement may make an arrest at any location, private or public.