A peace officer, when making an arrest without a warrant, shall inform the person to be arrested of his intention to arrest him, of his authority, and of the cause of the arrest.  A private person, when making an arrest, shall inform the person to be arrested of his intention to arrest him and of the cause of the arrest.

The officer or private person making the arrest need not so inform the person to be arrested if the person is then engaged in the commission of an offense, or is pursued immediately after its commission or after an escape, or flees or forcibly resists before the officer or person making the arrest has an opportunity to so inform him, or when the giving of the information would imperil the arrest.