What is meant by 'reasonable grounds' for belief in the context of a security guard's arrest powers?

1. Any information received from a third party, regardless of its reliability.
2. The security guard's personal belief based on their experience, even if lacking specific facts.
3. A hunch or intuition that something illegal might be happening.
4. A set of facts and circumstances that would lead an ordinary, prudent and cautious person to believe that an offence has been or is being committed.