Sometimes complicated issues can be made very simple. Here are some good reasons to think the Gospels are the preserved testimony of eye-witnesses from the 1st century. We will talk about the early second century writings of Papias, the introduction to the gospel of Luke, the riddle of names in the gospels and the issue of genre. All these elements are like arrows pointing to one big fact; the gospels contain the record of eye-witness testimony and attempts to treat them as though they are a hodgepodge of rumor which are far removed from the original sources simply fail.
Jesus and the Eyewitnesses - excellent book by Richard Bauckham https://amzn.to/2TWYuzz (this is an affiliate link)