Final answer:
The guard should not arrest the person but should monitor the suspect and write a detailed report.
Step-by-step explanation:
Based on the options provided, the correct course of action for the guard is option 3. The guard should not arrest the person because he did not personally witness the incident, however, he should monitor the suspect to see if they attempt to take anything else. If they do not, the guard should write a detailed report about the incident and seek if the customer can identify what items the shoplifter stole.
This approach respects the legal principle of innocence until proven guilty and avoids false accusations or violating the suspect's rights. It is essential for the guard to gather more information and evidence before taking any further action.