The film stars a great cast along with Rod Steiger, Sidney Poitier, Lee Grant, and the very underrated but so talented Warren Oates. It is a simple murder investigation with a twist, it's in a small southern town in the 1960's that is heavily segregated and the main investigator a black police officer from Philadelphia. The acting is magnificent and is full of suspenseful drama.
But it is the social overtones that define this movie. Rod Steiger is a police chief who is caught between doing things the old way and pleasing the establishment and having to accept that Sidney Poitier's character knows more than him and is the only way for him to solve this case. This delicate balance he attempts is why he won Best Actor. And Sidney Poitier is great as usual.
The other significant reason why I choose this film to comment on is the doorway it opened to future Best Picture winners of the next decade. This ended the era of musicals and epics winning Best Picture and started the era of the gritty drama or movies that didn't always have a happy ended. In essence, the Hayes code was over. From this point on, with rare exception, this was the type of film to be nominated and win Best Picture.
Personally I think it was the best thing to happen. The quality of movies from this era of the late 1960's and early 1970's are some of the finest to be made. The only other era that could compare and you could claim was better would be the mid to late 1930's and early 1940's. And of course the clip for today has to be the great "They call me Mr. Tibbs" scene.