The Great Gatsby, watchers

I'd like to know if "watcher" in the following excerpt from the chapter Eight of The Great Gatsby means "onlooker" or "one who watches by the dead" or both of them?

By six o’clock Michaelis was worn out and grateful for the sound of a car stopping outside. It was one of the watchers of the night before who had promised to come back so he cooked breakfast for three which he and the other man ate together. Wilson was quieter now and Michaelis went home to sleep; when he awoke four hours later and hurried back to the garage Wilson was gone.