Which of the following is a valid reason for making a warrantless arrest?

A warrantless arrest is typically justified when a police officer has probable cause to believe that a crime has been committed and the crime is observed directly by the officer. This is rooted in the concept that the officer needs to act swiftly to prevent further criminal activity or to ensure the arrest does not escape.

When an officer witnesses a crime in progress, such as committing an act in their presence, this gives them the immediate authority to make an arrest without needing a warrant. The presence of the officer establishes probable cause, making the arrest valid and legally sound.

Other options do not provide valid justifications for warrantless arrests. For instance, issuing a notice to appear for minor traffic violations typically doesn't warrant immediate arrest, and holding an individual for someone else's alleged crime usually requires more evidence and is not permissible. Additionally, merely requesting identification does not equate to probable cause for arrest. Thus, making an arrest based on witnessing a crime aligns with legal standards for warrantless actions.