Se7en - Narrative Theory

Se7en is 1991 psychological horror movie which stars Brad Pitt and Morgan Freeman. It was directed by David Fincher.
 
This is as a closed narrative movie. This is because we do not know who the killer is and why he is performing such awful crimes. We know as much as the detectives do at any moment which adds to the suspense of the film. This is because we don't know if they've missed something and when they notice that they have, the surprise is also given to us. If this film was open narrative I don't think it would of had the same effect because we would know why John Doe (Kevin Spacey) was killing these people and also we'd know the victims. Knowing who the victims are would ruin the twist and shock ending and would make the film quite mediocre in my opinion.
The first murder was revealed to the audience as a simple killing; it's only a few scenes later when we find out this crime had a motive and there should be 6 more murders to follow (according to the Seven Deadly Sins).
The sins are given to us in the order of gluttony, greed, sloth, lust and pride before they actually manage to detain Doe. What is confusing to the audience is how he gives himself up very easily in the lobby of a busy building. He's covered in blood and is not hiding himself when before he was. This then makes it obvious that this is part of his master plan to kill of the sins.
However, before the 4th murder - lust - Detective David Mills (Brad Pitt) and Detective William Somerset (Morgan Freeman) manage to track down John Doe and get to his apartment. A fight then ensues causing Mills to become angry and sloppy with his chase - giving Doe the upper hand. Doe has a chance to kill Mills but only pistol whips him instead. In a weird way, this could be a foreshadowing to the ending because to Doe all this isn't over yet - even when he is in prison.
As it was a sort of murder mystery movie - it followed a lot of conventions which are present in the crime genre. For example, the crime scenes which were explicitly graphic and quite horrific. They included such conventions as evidence, blood and police. This makes it obvious to the audience that something horrible has happened and what the genre actually is.
In conclusion, the narrative for Se7en is quite clever as if everything was known the film would not have the same effect as it does because it is a closed narrative.