One critical error prevented this from being a great movie

Rating: 7/10 (6 May 2018)

Trying not to "plot spoil" -- was going to wax on, as to how this was one of the 30 best movies that I have ever seen, because of the great acting, the compelling story line and the intense moments that emanated from the film.
Then the movie ended and I went.................. "Oh, No!"
This movie had the potential to be great, and that director just trashed out the movie at the end. I cannot believe that I am the only viewer who was disappointed. I really hope that future movies do not capture this format.
You cannot have a murder mystery, and end the movie without identifying "who dun it?" Movies of this type, have one description....."a waste of time." Even still, I got to rate it a 7 because the movie was so good, in so many respects.