Zero can be considered the point at which a crime occurred. It may be murder, kidnapping, assault or theft. The point in time at which it took place is most important both in real life and in fiction.
This zero hour or zero point is the moment in time when the investigation begins. Events leading up to it , also called the backstory, must be looked into. All that happens after the crime is also important. However , the reference point for all this is Point Zero.