Actually, the thief was baptized. Baptism is a symbol of crucifixion of the flesh and resurrection to newness of life. The thief was "crucified with Christ" and so was baptized for "real". We only experience symbolically what the thief and the Lord experienced in reality.
Note that in the following verse Jesus clearly identifies crucifixion and baptism:
Mark 10:38 But Jesus said to them, "You do not know what you are asking. Are you able to drink the cup that I drink, or to be baptized with the baptism with which I am baptized?"
Paul does the same thing in this verse:
Romans 6:3-6 Do you not know that all of us who have been baptized into Christ Jesus were baptized into his death? We were buried therefore with him by baptism into death, so that as Christ was raised from the dead by the glory of the Father, we too might walk in newness of life. For if we have been united with him in a death like his, we shall certainly be united with him in a resurrection like his. We know that our old self was crucified with him so that the sinful body might be destroyed, and we might no longer be enslaved to sin.
Here is a link to information you will find helpful:
I hope you have found this helpful.