It determines how much information the reader has access to.
There are three different main categories for point of view. The most common are first person and third person. When a story is written in first person, the reader only has access to the information of the speaker. Whatever the speaker knows, the reader knows. Therefore if the speaker does not know who his killer is, neither will the reader. The reader may be able to piece together information faster than the speaker to make a guess, but will never know for sure. Third person point of view is when the narrator of the story is from outside of the story. The narrator is looking down on the action. In this case, the reader may or may not know more than the main character. Point of view can have a significant impact on the information given to the reader.
