Just something to consider - based upon your original question, "Who and when was the first believer in Jesus Christ resurrected to life?"
We can be absolutely certain that Christ Himself believed in His message, believed in His His Gospel and believed in His ultimate death to save all Believers... But, other than Christ himself, your thought about the thief is correct. Christ told him in Luke 23:43 (KJV), "43 And Jesus said unto him, Verily I say unto thee, Today shalt thou be with me in paradise."
The thief believed in a life to come through Christ, and desired that life. He was humbled in true repentance, and brought forth all the fruits of repentance -unlike like the other thief, to be only saved from his situation.