Camus' The Stranger is so tightly constructed that he has introduced most, if not all, major developments in the early parts of the story through foreshadowing, with the result that Meursault's experience--no matter how incredulous--is believable. This is because his inner traits are built firmly upon the qualities that foreshadow and eventually lead to his doom.
One significant example that foreshadows his crime is his habitual reaction to light, sun and heat. Meursault repeatedly narrates a description of these elements along with his reaction to them. Beginning on the first page, Meursault says, "It was a blazing hot afternoon" with a "glare off the road and from the sky.” He then states his reaction to the "blazing" heat and "glare … that made [him] feel so drowsy."
This foreshadowing, embodied as it is in the motifs of heat and sleep, repeats throughout Part I of the novel while increasing in intensity with each passage until Meursault walks alone on the beach and experiences the heat climbing to a climax around him:
And each time I felt a hot blast strike my forehead, ... I clenched my fists ... and keyed up every nerve to fend off the sun and the dark befuddlement it was pouring into me.
The foreshadowing is fulfilled when the climax arises when the "cymbals of sun" and "fiery gust" make "the sky crack in two" releasing a "great sheet of flame" that makes every nerve in Meursault's body jump thus causing his grip to tighten on the revolver. One additional step in the fulfillment of the foreshadowing of Meursault's doom comes when he responds to the judge's question about "what were the motives" of his crime by explaining "that it was because of the sun."
As incredulous as this sounds, and however many people he heard "tittering," the reader believes Meursault because the foreshadowing has established the credulity of Meursault's experience from the beginning of the story.
Some other examples of foreshadowing are Meursault's employer's annoyance at him, foreshadowing the jury's and judges' extreme annoyance with him; the idea of "fault" foreshadowing his eventual feeling of remorselessness; and Meursault's agreement to write Raymond's letter for him foreshadowing the later accusations of immoral heartlessness during his trial.