I saw this movie way back in the 80s and can't find a name to it. From what I remember, it has the following:
- Alien on the run on Earth
- Alien cop chasing him
- Alien cop reveals himself/is caught by human police after being wounded and declaring "I'm a cop, like you"
- Human cop decides to help out
- Alien on the run attacks people by injecting a liquid into them, and sucking out a sample of their blood with a tube/needle arrangement - can't remember why though, and I think he injects this sample into the next human and so forth
- Most victims are male and I think one was female.