Good Thief

Good Thief or Penitent Thief, in the New Testament, the malefactor crucified with Jesus who did not revile Him; Jesus promised him Paradise that day. In the Roman martyrology his feast is Mar. 25. His name in tradition is Dismas or Desmas, that of the other thief Gesmas.

thief the Good Thief a traditional name for the penitent thief, St Dismas.
set a thief to catch a thief proverbial saying, mid 17th century; in an epigram the Greek poet and scholar Callimachus (c.305–c.240 bc) has, ‘Being a thief myself I recognized the tracks of a thief.’ The saying is used to imply that the person best placed to catch someone out in dishonest practices is one whose own nature tends that way. (Compare an old poacher makes the best gamekeeper.)
when thieves fall out, honest men come by their own proverbial saying, mid 16th century; meaning that it is through thieves quarrelling over their stolen goods that they are likely to be caught, and the goods recovered. The shortened form ‘thieves fall out’ is used to imply that an association based on shared dishonesty is likely to be disrupted.

See also hang a thief when he's young, there is honour among thieves, little thieves are hanged, opportunity makes a thief.

Penitent Thief see Good Thief .