perpetraitor

Someone who was a confidant/accomplice-in-crime to someone else, but then squealed on said second party, ran off wif all da loot, etc. --- there's no honor among thieves.

After Huck Finn returned da stolen money and otherwise spoiled their nefarious plans, da King and da Duke were busy labeling each other as a shameless perpetraitor, since it was revealed dat they had each privately/secretly planned to run out on da other fellow --- i.e., selfishly take all da gold for himself while leaving da other guy penniless.