It's most likely that Luke interviewed as many people as he could as he was compiling notes for the most excellent Theophilis. I do believe that Luke got first hand information from the first apostles, I mean the likes of John, Peter, Paul, Mathias, etc. This man must have gone an extra mile to prove every bit of information he obtained therefore he moved to varoius places of Israel, Judea, the far East and the Roman empire were Jesus and first the apostles reached especially Paul. However, like every physician, they do not believe a lot in super natural powers, little wonder that Jesus is so much reffered to as a Son of Man in the book of Luke than any other book in the new testament. All the facts about Jesus as written by Luke are also written in other books of the bible, like Matthew, John, and Mark, therefore, he did enough homework, which he later edited to exclude facts that most physicians feel that they do not apply in world of humanity and science.