Here is a show that was recently taped for ABN Apologetics Marathon. In this show, myself along with some others in the apologetic field discuss the death of Jesus. You will see about halfway through the show, a Muslim apologist gives his reasons for rejecting our reasons for the historicity of the death of Jesus.
As I note in my reponse to him, the Greek word for “eyewitness” (autoptai) refers to those that would have participated in the events (direct autopsy). If the authors didn’t participate in the events they were writing about, they sought informants who could speak from firsthand knowledge and whom they could interview (indirect autopsy). For example, since it is obvious that Mark relies on Peter as a direct eyewitness, Mark’s Gospel is a form of indirect autopsy.
We see in Luke 1:1-4 that while Luke was not a direct eyewitness of Jesus’s ministry, and the information was given to him by those who “from the beginning were eyewitnesses and ministers of the word,” he also is a form of indirect autopsy. Space prohibits a robust defense of John and Matthew’s Gospels, but since John claims to be a direct eyewitness (John 21:20-24) he is form of direct autopsy. Matthew’s frequent references to money remind us that he had been a tax collector. It is likely that this role is an example of a direct eyewitness to the ministry of Jesus as well.
As far as Paul, once again, for the historian to have been himself a participant in the events is a form of direct autopsy. Failing that (and no historian was present at all the events he need to recount, not least because some would be simultaneous), they sought informants who could speak from firsthand knowledge and whom they could interview (indirect autopsy). In other words, “autopsy,” is a visual means of gathering data about a certain object and can include means that are either direct (being an eyewitness) or indirect (access to eyewitnesses). Indirect autopsy is arguably used by Paul (1 Cor.9:1; 15:5–8; Gal. 1:16), Luke (Acts 1:21–22; 10:39–41) and John (19:35; 21:24; 1 John 1:1–4).