In Sophocles' Oedipus Rex, when does Oedipus begin to think that he himself is the murderer of Laius—what details lead him to this conclusion?
In Sophocles' Oedipus Rex, details from Tiresias and Jocasta are what finally convince Oedipus that he has murdered the former King of Thebes.
Creon has learned that the kingdom of Thebes is cursed because the lawful King of the city was murdered. Oedipus, trying to help his people by bringing an end to the outbreak of plague, the loss of their crops and death of their animals, calls for Tiresias (the prophet) and asks for his help. Tiresias argues extensively with Oedipus, desperate to leave and say nothing. It is not until the King accuses the prophet of treachery that Tiresias tells Oedipus what he demands to hear.
…I say to you: Abide by that decree
you made earlier, and from this day address (370)
neither these men here nor me, since you
are the unholy polluter of this land.
In essence, Tiresias tells Oedipus that he is the murderer, the cause of all the suffering in Thebes. Almost in riddles, Tiresias continues, half-explaining that Oedipus has done more evil than he can even imagine. (Here he alludes to Oedipus' sinful marriage to his mother and to the children he has fathered with his mother—his children are actually his siblings...but still Oedipus does not yet understand the significance of what Tiresias has struggled to keep secret.)
Oedipus sends Tiresias away, angry at his veiled accusations. He fights with Creon as well, accusing him of conspiring to take his throne from him. When Oedipus and Jocasta are finally alone, she tells him a story to show that the gods will reveal what prophets and seers sometimes do not. She believes the oracle that prophesied her husband's death at the hands of their son was wrong; however, as she speaks to Oedipus, her words strike a chord of horror in his heart.
A prophecy came to Laius once…
that death would come to him from his child,
whoever was born to him from me. But then,
just as the report is, some foreign brigands
slew him where the three wagon-roads meet.
Yet three days had not passed from the birth of my child, (745)
when that man, binding his ankles together,
sent him in another’s hands into the wild
of the mountain. And so Apollo brought about
neither that he slay his father nor that Laius
suffer the terrible thing he feared from his child.(750)
In hearing what Jocasta has said, especially about Laius being killed where three roads met, Oedipus asks her questions as to the town where her husband died, what he looked like and who was with him. All the details lead Oedipus, tragically, to believe that without knowing it, he did in fact kill his father. (Still Jocasta knows nothing of this.)
When Oedipus asks how she knew of any of the details of Laius' death, she reveals that there was one survivor, and Oedipus, looking for the final damning piece of evidence, asks his wife to summon this man who has left the city to become a shepherd once more.
Meanwhile, a messenger arrives from Corinth to tell Oedipus that his "father" is dead, but reveals...
...Polybus is nothing to you by birth! (1043)
Oedipus had fled his father's house for fear of killing him, only to end up where he would kill his biological father. The messenger and the shepherd meet, and it is discovered that the shepherd gave Oedipus to the messenger (a shepherd then) to save the baby's life. All that Tiresias inferred was true, and Oedipus knows that the prophecies were not false: he is the monster the prophet accused him of being, cursed from his birth.