This was one of the few times that Alfred Hitchcock filmed one of his stories as a "whodunit" in which you are not sure until the end who committed the crime. "Murder!" is often slow-moving, but it has some good features, and is worth watching the whole way through. It was one of Hitchcock's earliest sound pictures, and he tried some new things here, some of which work quite well.
Herbert Marshall stars as Sir John, a famous actor who sits on a jury for a murder case. After the case is decided, Sir John starts having second thoughts over whether the verdict was really correct, and he decides to investigate on his own. His investigation itself moves rather slowly, but it has some entertaining moments. Everyone connected with the murder was part of a theater group, and Hitchcock gets some good mileage out of having the characters alternate between their real identities and their stage roles. There are some pretty good scenes, most especially the one of the jury's deliberations - it is quite amusing, and a not-too-subtle example of Hitchcock's lack of confidence in the infallibility of the legal system.
There is not very much of the suspense for which Hitchcock is famous, but instead there is some subtle humor and a lot of atmospheric detail. While not having the sustained excitement of Hitchcock's best films, "Murder!" is still worthwhile as a slightly different kind of film by the great director.
