Mr. Wargrave was the leader of the group while they were trapped on the island. He took up this role because he knew what he was going to do later in the book. He said that he wanted to,"...take care of the cases the courts cannot touch." He was not right in his mind and thought that he needed to kill the people that never got punished for their "crimes".
He made many assumptions about the "killer" which led the others to drift apart from each other. This