''The person I killed'', the person is an object, so omit the pronoun ''who'' is right, but in The Invisible Man chapter 28: He stood up abruptly and then knelt down on the ground by the side of the thing unseen. The thing is an subject, but it still omit the pronoun ''which''. ''...by the side of the thing which is unseen.'' Chapter 28 too: so that veins and arteries and bones and nerves could be distinguished, the outline of a hand, a hand limp and prone. Omit the same thing. Does that mean it is wrong? I think it should be ''...the outline of a hand, a hand which is limp and prone.''