They can to a certain degree. And most people will follow the law rather than deliberately break it. At the moment though, the majority of the public is probably unaware of what can and can't be said in order to avoid prejudicing someone's trial. Also, remember that this crime has been big news in Melbourne but in other parts of Australia, and possibly even Victoria, most people have not been following it closely on Facebook etc. Her remembrance page on FB only had 44,000 "Likes", so it's highly unlikely that an impartial jury could not be found, IMO.