Hi. I'm looking for a title of a movie that I watched in the early nineties (so the movie may be from late eighties) about aliens. One was a criminal that escaped from transport and the other was an alien police officer. I remember that the criminal was some kind of drug addict; he was catching people and injected them with something and then he took some of his victim's blood (I guess that he took blood by sticking a needle in the victim's forehead and injected sth straight into the heart). The police officer had this weapon that basically looked like a sharp magnetic CD. I don't remember much but I guess that the good alien died and human law enforcement had to catch the bad alien. That is basically all I remember. Does anyone know what movie I'm talking about?? Help. And thanks in advance.

This is probably what you're looking for:

I Come In Peace (http://www.imdb.com/title/tt0099817/)

Thanks I's exactly what I was looking for