I'm searching for a movie that I saw as a child. The movie is about an investigation for an alien killer. The main character was a male detective who tried to understand what is happening. There was some exotic weapons, what I remember is a razor gun that used by the aliens. The gun shot rotating razor discs that never stopped rotating (and bouncing). The detective found a projectile trapped by a speaker's magnet. The guns used some white fluid in small transparent containers as ammunition.
There is a huge possibility that my memories are not perfect, but the key to find the movie is that razor gun.