Is Oedipus innocent in Oedipus Rex?
Yes and no. There are obviously two angles you can take on this. Firstly, literally Oedipus is a guilty man, and the play centres on his determination to find out the guilty man only to discover that it is himself he is looking for all along. He admits his guilt when the truth, which the audience are aware of, comes crashing down after his interview with the Shepherd. Note what he says at this moment of epiphany:
all come true, all burst to light!
O light--now let me look my last on you!
I stand revealed at last--
cursed in my birth, cursed in marriage,
cursed in the lives I cut down with these hands!
This is clearly unequivocal, as Oedipus recognises that he is the murderer he is looking for and describes himself "cursed" as a result.
However, you could also equally argue that Oedipus is a character who does not have free will. His life was mapped out for him by prophecy before he was born. As a result, to what extent can be apply terms such as "innocent" and "guilty" to him? Can he really be judged as being "guilty" by the laws of man when divine providence dictated that he was going to kill his father even before he was born? To what extent can he be held accountable for carrying out an action that it was fated he would carry out in complete ignorance? This is one of the central questions behind this play, as we are forced to ask ourselves to what extent Oedipus as a character has free will or not, and how we should judge him as a result.
I assume you're looking for source material. Your librarian should be able to help you locate scholarly journal articles and essays on this subject. If your school does not have access to sites like JSTOR or EBSCOhost, you can try a public/state University or community college, as they often offer these services, and their libraries are public.