Final answer:
The correct 10-letter word for a partner in crime is 'accomplice', which indicates someone involved in assisting another person in criminal activities.
Step-by-step explanation:
The 10-letter word that refers to one's partner in crime, perhaps as an accessory, is 'accomplice'. This term is commonly used in legal contexts and refers to a person who helps another in committing a crime. The scenarios described might be seen as reminiscent of the classical Prisoner's Dilemma in game theory, where two individuals must choose to cooperate with or defect (betray) each other without knowing the other's choice, with various potential outcomes based on their decisions.