That's a good point. However, I think the thief on the cross really did commit a crime. Whether he deserved to be shamefully and agonizingly crucified or not, I have no clue.

Jesus was a public enemy for the Jewish religious higher-ups, and he also threatened Rome on a smaller scale, and his entire ministry he garnered attention and derision from those people, so their midnight trial and illegal crucifixion of Him happened. However, with the thief, he was just a nobody, just some guy, which leads me to believe he really did get caught red handed, perhaps stealing from government officials or someone wealthy, thus earning himself a spot next to the Son of Man.

I have a sense that the writers of the Gospel who mention the thief would have included info about the man had there been anything else to say, as there were only two other convicts there at the hill of Calvary that morning.

Either way, whether he did steal or not, he was still a sinner, like you and me. And so Jesus pardoning him due to his faith still stands, and still has vast meaning for us.