Gospel writers who were not disciples of Jesus Where did Mark and Luke get information about life of Jesus to write Gospel?
Where did Mark and Luke get information about life of Jesus to write Gospel?

There is a very large field of study that attempts to put forth various theories of authorship by writing styles, word usage, and quite a bit of conjecture.

We do know of the twelve immediate disciples of Jesus. We also know of seventy others that were sent out on a particular ministry. It may be that there were even more. The criteria for being a disciple is given by Jesus;


  John 8:31-32  Then said Jesus to those Jews which believed on him, If
  ye continue in my word, then are ye my disciples indeed;  And ye shall
  know the truth, and the truth shall make you free.


We also have to consider that what was written was not just recording facts or gathering anecdotes.


  2 Timothy 3:16  All scripture is given by inspiration of God, and is
  profitable for doctrine, for reproof, for correction, for instruction
  in righteousness:


Eyewitness accounts may have been collected, but the final authorship depends on the guiding hand of the Holy Spirit.


  1 Thessalonians 2:13  For this cause also thank we God without
  ceasing, because, when ye received the word of God which ye heard of
  us, ye received it not as the word of men, but as it is in truth, the
  word of God, which effectually worketh also in you that believe. 
  
  2 Peter 1:21  For the prophecy came not in old time by the will of
  man: but holy men of God spake as they were moved by the Holy Ghost. 
  
  John 14:26  But the Comforter, which is the Holy Ghost, whom the
  Father will send in my name, he shall teach you all things, and bring
  all things to your remembrance, whatsoever I have said unto you.