Mix first six ingredients. Place roast in a 5-qt. slow cooker; add water. Pour ketchup mixture over top. Add cookie crumbs. Cook, covered, on low until meat is tender, 6-8 hours.

Remove roast from slow cooker; keep warm.
Strain cooking juices; skim fat.
Transfer 4 cups juices to a saucepan; bring to a boil.
Mix cornstarch and water until smooth; stir into cooking juices.
Return to a boil; cook and stir until thickened, 1-2 minutes.
Serve with roast.