According to them Shannon keeps seeing Walt and eventually figures out the creepy whispering is telling her to not let the others press the button. She tries telling the rest of the castaways this and they wont listen, and act as if she has gone mad. At the end of an episode she sneaks into the hatch to try to destroy the computer and is shot by someone offscreen. For several episodes it will be made to look as if Locke did it-but the audience eventually discovers it was actually Jack-yep Jack. The audience will be aware of it, but none of the other characters on the show will have any idea, and the writer even went as far as to hint that Locke will be driven away from the group because of it.