Wrong! Tiresias says the murderer of Laius is in Thebes, and will be proved to be a native Theban; he says that the murderer will be revealed as father and brother to his children. There's nothing that Oedipus need take as applying to him. The crossroads have not yet been mentioned: when Jocasta brings up the place where her husband was killed, only then does Oedipus begin to worry that he may have killed Laius (but not of course that Laius was his father!)