What evidence is there that the thief on the cross was not baptized?

In Luke chapter 23, there is an interaction between Jesus and two thieves on the cross. One of the thieves mocks the Savior, telling him to save himself. The other thief rebukes the first, and confesses that he deserves to be on the cross, but Jesus doesn't: > “And one of the malefactors which were hanged railed on him, saying, > If thou be Christ, save thyself and us. > > “But the other answering rebuked him, saying, Dost not thou fear > God, seeing thou art in the same condemnation? And we indeed justly; for we receive the due reward of our deeds: but this man hath done nothing amiss. > > “And he said unto Jesus, Lord, remember me when thou comest into thy > kingdom. And Jesus said unto him, Verily I say unto thee, Today shalt thou be with me in paradise” (Luke 23:39–43, KJV ). This passage is frequently referenced (sometimes along with others) as evidence that baptism isn't a prerequisite for salvation. However, it's not clear to me how this passage can be used to make that assertion. What evidence is there that the penitent thief was not baptized? (He already knew who the Savior was, so it would make sense that he had followed him at some point during his ministry.)