Oedipus discovered that his father died from being thrown from a fight with an unknown man. Later once rememering that situation sounds very familiar to him that he himself had unknowingly killed his father.
The audience feeling of pity and fear is when Oedipus calls upon Tiresias for Tiresias to tell him the truth of who murdered the king. Tiresias witholding the truth from Oedipus recieves much backlash and gives into hinting at his knowledge of the murderer.
The true Hamartia of Oedipus is the mistakes he has commited in his past. Unknowingingly killing his father in a fight on the road had essentially lead to his own demise. If Oedipus hadn't killed his father then his mother never would have become a widow and without her becoming a widow they never would've became intimate with one another.
Oedipus believed in himself so much as to the point where he thought as if he could defy his own prophecy. When in reality Oedipus's desire to not fulfill his prophecy lead him into the path of actually fulfilling his prochecy down to a tee.
Oedipus curses the murderer of the king not knowing that he himself is the murderer of the king.
The Blind prophet Tiresias can see the truth. Tiresias knew the prophecy of Oedipus ever since his early existence.