Thriller Idea 2 -

Opening Sequence - Long shots of a a normal looking man with a hat on and we follow him from behind pov, he walks through an office sort of seeming to be ignored. We see him walk through a busy foyer seamlessly with out being asked any questions, hopefully making the audience trust the guy we are being shown. We then see him knock on a door and hear a voice say come in, all this time still not seeing the face of the man who had knocked on the door, we come into a normal cop in his office, the man enters, and we see the man at the desk looking at the man who has just entered, he then asks the cop to solve a murder. When the cop asks who was murdered in a laughing sort of tone, the guy who has walked in says'We were,' and we are then shown a mid shot of the guy lowering his collar & taking off his hat to reveal that the client is the cop is himself, as a sort of ghost from his own future, trying to solve his own murder before it happens. 

Whole Film- The film would follow the cop trying to solve his own murder being driven by himself/ his ghost throughout. the ghost would make the cop question his trust with every person near or not so near and dear to him. Eventually driving him to near insanity and ending up with him trusting no one. It ends with him killing himself, which the ghost has been trying to warn him not to do all along but by him being so uptight he sort of drives himself to kill himself.