In this story, the suspense continues even after the story has ended because we do not know if Mrs. Salmon (and perhaps others) might be in danger from the murderer.
At the end of the story, one of the Adams twins is run over by a bus and killed. Of course, we do not know if it was the killer or the other brother. The living brother looks over the dead brother’s body, straight at Mrs. Salmon. The story ends with the line
“But if you were Mrs. Salmon, could you sleep at night?”
This leaves us in suspense. We do not know which brother lived and which died and we do not know if, by looking at Mrs. Salmon, he is showing that he intends to kill her.