You see, the thing is this, in the movie people confuse bateman for several different people (Davis, Halberstram, etc). This leads me to believe that he very well could have killed all the people, however, no one would recognize him due to the fact that they are always confusing him for other people. His own lawyer confused him for a guy named davis. Paul Allen (Owen in the book) confused him for halberstram. So, I think he could have killed the people and can probably get away with it due to the fact that everyone confuses him for other people. Heck, his own lawyer said he had dinner with owen/allen in london which leads me to believe he also confused the man he had dinner with for paul owen/allen.