None of the authors claims that. So how do you impose that upon authors who never claimed that?
John was written 70 years later. How could that be a first hand account?
Nevertheless, you said independent witnesses. But it was retracted. No problem. They are neither witnesses, nor were they independent.
"None of the authors claims that. So how do you impose that upon authors who never claimed that?"
That is a fair critique. None of them speak very explicitly about being eyewitnesses or about who their sources are. Several do make claims to have been eyewitnesses to an extent, however.
Paul claimed to have seen the resurrected Jesus.
"Am I not free? Am I not an apostle?
Have I not seen Jesus our Lord?" (1 Co 9:1 ESV).
"Last of all, as to one untimely born,
he appeared also to me." (1 Co 15:8 ESV).
John: "He who saw it has borne witness—his testimony is true, and he knows that he is telling the truth—that you also may believe" (John 19:35 ESV).
The author doesn't explicitly say that "he who saw it" is himself, but it's seems pretty clear that he is implying that.
I'm not aware that the author of Matthew makes any claims to have been an eyewitness.
Luke has this interesting introduction:
"Inasmuch as
many have undertaken to compile a narrative of the things that have been accomplished
among us, 2 just as
those who from the beginning were eyewitnesses and ministers of the word have delivered them to us, 3 it seemed good to me also, having followed all things closely for some time past, to write an orderly account for you, most excellent Theophilus..." (Lk 1:1–3 ESV).
This does not definitively prove anything, but it has some interesting statements... Luke claims that "those who from the beginning were eyewitnesses and ministers of the word" delivered a report of the "things that have been accomplished among us." Is he referring to written or oral accounts? I'm not sure. Either way, he is claiming to be reporting information passed on by eyewitnesses. It's also interesting that he says "the things that have been accomplished
among us." If he was writing this long after the events had taken place, it wouldn't make much sense for him to say it this way. If that is the case, he could well have been receiving the reports of the events from eyewitnesses. I don't know. I haven't thought through it entirely.
"John was written 70 years later. How could that be a first hand account?"
Sure, I think from 50-75 years later would be a common estimation. That is not unreasonable to have been an eyewitness account. If it was really John, he could easily have been around the age of 20 at the time when he was with Jesus, so while he would have been old, it is not out of the question.
"They are neither witnesses, nor were they independent."
What do you mean by "independent"? What to you is an independent source?