Well we only have the word of the author of Acts that there were any eye witnesses. He may have invented them to add weight to the story.
Here's what the author wrote at the beginning of his first book to Theophilus. The missing words here point to reliable testimony:
"Many have undertaken to draw up an account of the things that have been fulfilled among us, just as they were handed down to us by those who from the beginning were e_________s and s______s of the word."
"Therefore, since I myself have c_______y inv_______ed everything from the beginning, it seemed good also to me to write an _______ account for you, most excellent Theolhilus, so that you may know the _________ of the things you have been taught".
PS, we could contrast your statement, "the eye witnesses don't really exist."