Continuity mistake: When Eddie is hiding with the golf club, there is a blue chair which got knocked over during the murder. But a few minutes later when Eddie is peeking round the corner to check for intruders, the blue chair is magically standing upright again.
Continuity mistake: When Eddie is eating breakfast and waiting for Van Loon, his hands and the food he is holding change position repeatedly between shots; sometimes his hands are down, sometimes they are holding up some food, and the amount of food he his holding changes too.
Continuity mistake: At the beginning of the movie, when the shot pans up the front of Eddie's building from street level, there is a balcony a few levels before we reach the top. When Eddie looks down from where he is standing and we see the front of the building from his point of view, the balcony is no longer there; the front of the building is now completely flat.
Continuity mistake: When the fight in the apartment occurs Victor is choking Eddie. At the start of the scene the dish sponge he eventually shoved in Victor's mouth is resting beside the sink. When the camera angle changes the sponge is in the sink. When Eddie grabs the sponge it's next to the sink again. (01:20:52)
Continuity mistake: In the restaurant scene at the end of the movie Eddie's flag lapel pin is right side up. The camera cuts to the waiter and when it cuts back to Eddie the flag pin is upside down.
Continuity mistake: Before Eddie dives in to the sea, the sunshine is indicative of midday, but when he is swimming it's more like evening.
Answer: Although there is no definitive proof, I believe the killer to be Atwood's henchman. During the trip scene we see him following Eddie and the Blonde to their room and although it comes off as an illusion there's no reason it cannot be real. This alone is not enough to say for certain but the main reason I point to the henchman is because of how the story plays out following the murder. Eddie is by an eyewitness (probably someone working for Atwood if not the actual killer) who tells the police about him and as a result he is called into questioning. Because of the inquiry Eddie hires "the best lawyer in the city" who as we know is under Atwood's thumb. It is during this line of questioning the lawyer is able to go into Eddie's jacket and steal his NZT. None of these things would have happened had the Blonde never been killed.
dream3ater