An important purpose of foreshadowing in mysteries is to develop the main characters. This in turn will help the key characters appear more like individuals with an outcome to come. Foreshadowing can be applied by making statements regarding each character's feelings, plans and thoughts.
Foreshadowing is used as a way of creating suspense in a mystery. Creating suspense will help to draw readers into the story through anticipation. Foreshadowing tools for suspense work by providing moods, settings, events and characters that are moving toward an unknown yet certain climax.
Along with character development, another purpose of foreshadowing is to convey bits of information that will help the reader understand what is to come later on. Unlike suspense, the information is conveyed in a way that readers will expect a certain outcome in parts of the story as the mystery continues.
Also known as "red herrings," another purpose of foreshadowing is to leave false clues or misleading information. This works well in mysteries as readers are led to believe that one character may be the guilty party, when in fact another one is. In order to keep the antagonist a mystery, writers often use literary trickery to misdirect readers.