You can't, hasn't been possible to be locked in a freezer for years, not unless they put a hasp and lock on the freezer and even then someone else would have to do the locking. And besides that, what kind of an idiots would lock themselves in a confined area if they were afraid of someone with a gun?
“And besides that, what kind of an idiots would lock themselves in a confined area if they were afraid of someone with a gun?”
Only people who have never worked at a restaurant would say or believe this.