Final answer:
The thief's __________ escaped would be considered the accomplice.
Step-by-step explanation:
The correct answer to the question is accomplice.
An accomplice is a person who helps another person commit a crime or illegal activity. In this context, the sentence is referring to the thief's partner in crime who managed to escape capture.
For example, if two people rob a bank together, one person may be caught by the police, but the other person who managed to get away is considered the accomplice.