Oedipus, ruler of Thebes, murdered his father and married his mother. Such acts are almost always deemed unnatural and criminal; they are not tolerated within traditional society. A person who has committed these illegal acts of murder and incest would be considered a criminal, yet Sophocles's character, Oedipus, is not guilty of either crime.
Prior to the birth of Oedipus, a prophecy was spoken over Laius and his wife Jocasta. They were told that their son would one day be his father's killer and would then marry his mother. In fear, King Laius and Queen Jocasta sent the baby Oedipus off with a slave to be killed. He was never killed, but rather was given to a childless king and queen which lovingly raised him. Oedipus was never factually told about his lineage. Later in his life, Oedipus was confronted by several unknown men while traveling. Upon confrontation, Oedipus killed all but one of the men in self defense. Unknowingly, Oedipus had begun to fulfill the prophecy for one of the men had been his birth father, Laius.
While still traveling, Oedipus had come to the city of Thebes. There, he saved the city from the wrath of the Sphinx by solving her riddle. Seen as a savior by the citizens of Thebes, Oedipus was made king and subsequently, the husband of Jocasta. Oedipus and his wife-mother ruled together and had four children while never knowing of the true relationship between each other.
As the tragedy comes to a close, the truth is revealed to Oedipus concerning his lineage and unnatural actions. Although the truth had been spoken to him about these matters previously, Oedipus had chosen not to believe and understandably so. True revelation comes to Oedipus through the same slave that had been ordered to kill him as a baby.
Since Oedipus had no knowledge of his birth parents, he cannot be accused of knowingly fulfilling the prophecy. He had no understanding of Laius as his birth father upon killing him. One might say...