The biggest mystery in this thriller is why did the credits start to roll 7 minutes before the end? Did someone say 'Oh damn, we still have 7 minutes to kill (pun intended), maybe we should add a postscript showing who the killer is.' That was actually unnecessary as there was no doubt who did the dirty deed. The writers throw in a few threatening characters to throw off the audience, but, sorry, not gonna happen.
What would I do to improve the story? Instead of peeing in the sink which she will never notice, have him pee in her orange juice...THAT will get her attention. Instead of just slinking around her apartment, have the killer rearrange her furniture, hang her pictures upside down...THAT will get her attention. Expand the nude scenes as the heroine has a killer bod. Heck, even expand the boyfriend's nude scene as he has a killer bum...THAT will get our attention. If none of that works, put the closing credits at the beginning of the movie so we don't have to suffer through 90 minutes of nothing happening.
Since not much happens for the majority of the movie, I spent the time wondering what the heroine would look like without collagen injections. What did I learn from this flick? Dogs make much better protectors than cats.