James Hrivnak’s review published on Letterboxd :
For whatever reason, I was hoping James B. Harris' Cop would be one of those forgotten gems—a film in need of re-evaluation and recuperation, like Don Seigel's Charley Varrick. Yet, for every Charley Varrick, you end up sitting through a dozen films that have been forgotten with good reason.
Based on the James Ellroy novel Blood on the Moon, James Woods plays your standard unorthodox cop of the 80s. He pushes boundaries, breaks rules, and (you'll probably guess) gets suspended from duty—all in the line of gettin' the job done— in this case, tracking down a serial killer. Woods' Lloyd Hopkins, though, is thoroughly unlikable and an a-hole. Which, I suppose, would be fine, if the film that supported him wasn't so dreadful.
Cop is a bore with weak plotting, lapses in logic, a laughably awful performance from Lesley Ann Warren (as a feminist bookstore owner), and long stretches where very little happens occasionally punctuated with grim violence.