of Mice and Men

George wants the men to believe that Lennie has taken the luger. He doesn't want the other men to torture and kill him with malice. He takes the gun and uses it in much the same way as Carlson used it on Candy's dog. It enables him to take Lennie's life in what he believes to be a merciful manner. The fact that the men believe that Lennie took the gun allows George to do what he sees as necessary without question.