Why did the witness to Laius' murder leave the city?

The witness to Laius' murder left the city primarily out of fear for his life upon seeing Oedipus as the new ruler. After the event of the murder, the witness knew that he held critical information that could implicate Oedipus, as the revelation of Oedipus’s involvement in Laius’s death would put his own safety at risk. The political climate in Thebes was already unstable following Laius’s death, and with Oedipus emerging as a powerful figure, the witness may have perceived that reporting what he knew could lead to his own demise. Leaving the city was a way to avoid confrontation and live without the looming threat of accountability for his knowledge of the murder.

The other options do not accurately capture the motivations of the witness. He wasn't punished for witnessing the murder; his fear was centered around the potential repercussions he could face as Oedipus solidified his power. Seeking vengeance on Oedipus does not align with the character's motivations, as he was more focused on self-preservation rather than revenge. Finally, there is no indication that he was called to serve in another kingdom; rather, his departure was strictly motivated by fear, making that scenario unlikely.