I think that if Mrs. Maloney tried to do this in our society then she would have definitely not of been able to get away with it. The detectives would try and get closer to the wife and make sure that she would not get away with it.
In my own opinion she probably been able to get away with it because she got rid of the blood stained leg of lamb and she did not kill him in a way that can be traceable. She was able to think right on her feet and quick. She planned this out very well.