Did anyone witness the killing of King Laius?is from the play oedipus.

You could answer this question in a couple of different
ways.

First, there is clearly someone who was present when King
Laius was killed and who survived the attack.  We are not told exactly who the person is, only
that he was either a messenger or a fellow traveler.  The person said that a large number of
bandits attacked King Laius and his people and killed them.

Another
way to answer the question is to say that there was no real witness.  The person who was there
saw what happened but essentially knows (or will admit) nothing.  He says that he can tell them
nothing other than that bandits were responsible.  He did not see who they were or anything like
that.  So in that sense, you could say that there is no useful
witness.