This is like saying that of course people could tell Ted Bundy was a psychopath, it always shows.

One might insightfully argue the whole point of the psychopath is precisely that it doesn't show. I recommend Cleckley, whose definition is seminal in The Mask of Sanity, [1] originally 1941 but prefer his 1988 fifth edition especially for its rather disconsolate preface. But even a cursory review of either will trivially show the comparison does not hold.

[1] https://gwern.net/doc/psychology/personality/psychopathy/194... - despite the filename, this is the 1988 edition. I like my paper edition (I made my paper edition) but the PDF will serve well enough for your reference here.