I can't disprove what, exactly? I think the only claim we have seen of an eyewitness account so far is that of the Letters of Peter. Well, there are some fairly obvious problems with those. The original writing was in an urbane style of Greek, and references the Septuagint translation, which was specifically for Greek Jews who couldn't understand Aramaic or Hebrew. So that's the first problem, what on earth would Simon Peter be doing writing in that kind of Greek, citing a translation he would never have read? If he is a witness to Jesus, there are no convincing personal details of someone who had spent time with Jesus. The text strongly suggests two different authors, so even if we accept that one of the authors was Simon Peter, you wouldn't know which of the writing was that of an eyewitness and which wasn't, since one of the authors is obviously anonymous.You mean you cannot disprove it.
Or were you thinking of some other author?
Stuart