Odd narrative choices? Why would I reveal the killer at the very beginning?

Why would I reveal the killer at the very beginning?

(Se7en, 1995)

Whilst creating the narrative for my opening scene, I chose to treat it as if I was planning a film two-hours long so that I could fully flush out and accomplish the first two minutes in the way that I want to. So I knew that there were multiple ways in which I could start a thriller movie, either present the audience with a murder, a crime scene or meeting the detective/main character. But instead of creating a conventional film, I chose to oddly focus on the killer. Not a murder, but a killer getting ready for the day, which makes the opening scene all the more unique and uncomfortable for the audience. 

However, the reason why I chose to go with this was because the main character is the killer, and whilst it is not uncommon for films to introduce the main character at the very beginning, it is certainly not normal to introduce a murder this early on. For example, in the film Se7en, John Doe is not introduced until there is only roughly 30 minutes left, in which he reveals himself to the police in a dramatic and shocking scene.

(Se7en, 1995)

So I think that introducing a killer right on the spot at the very start of a film is quite unsettling, especially as this would be a character that we would later follow for the rest of the film. I also think that an interesting approach to revealing the main antagonist (/protagonist) would be refreshing to anybody in the audience who expects the same formula of thriller movies again and again, and hopefully this will make my film more interesting and stand out. This is why I chose to take my film down such a strange narrative direction.