Please help me find this film

I remember watching this in 1985/1986. Could have been released earlier, but it felt like an 80's movie.

All I remember, was alien creatures transforming themselves into human beings by attacking them first. One scene was an alien attacking a policeman at his police car, and they fall to the ground, and next scene you see the alien being the policeman in his skin. That scene was at night time.

Been looking for it forever.
Thanks for any help.