Laura Palmer was killed by an evil spirit named Bob, who possessed her father, Leland Palmer. Under Bob's influence, Leland sexually abused Laura for years, leading her down a path of corruption and despair. On the night of her death, Bob, using Leland's body, stabbed Laura to death in a fit of rage after she resisted possession by wearing a protective ring given to her by Mike, Bob's former associate. Laura's body was then dumped on a riverbank, wrapped in plastic. Leland, possessed by Bob, was the direct killer, but the true evil behind the murder was the malevolent spirit Bob

. In summary, while Leland Palmer physically killed Laura, it was Bob, the supernatural entity possessing him, who was the ultimate cause of her death