If you mean the thief on the cross, someone mentioned that earlier. The thief died before the death, burial and resurrection of Christ. Obviously the thief had courage and honesty. He rebuked the other robber. He certainly appeared to fear God, and he acknowledged his guilt.
Jesus' teachings of the necessity of baptism for salvation was not given until He gave His great commission:
Matthew 28 18Then Jesus came to them and said, "All authority in heaven and on earth has been given to me. 19Therefore go and make disciples of all nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit, 20 and teaching them to obey everything I have commanded you.
Mark 16 15 He said to them, "Go into all the world and preach the good news to all creation. 16Whoever believes and is baptized will be saved, but whoever does not believe will be condemned.
Luke 24 46 He told them, "This is what is written: The Christ will suffer and rise from the dead on the third day, 47 and repentance and forgiveness of sins will be preached in his name to all nations, beginning at Jerusalem.
The thief never lived and died before this commission; therefore baptism was not applicable.