The mandate of heaven is the thing that Chinese emperors claim was given to them by their deities. A ruler earns it from the previous emperor when he retires, or when he dies. It could be lost when another dynasty takes over and takes the mandate of heaven.
Is is a question about what they help the criminal to do or whether the statement is true?
The statement is true: an accomplice does help a criminal, and does so knowingly. Together, they commit a crime or wrongdoing (in case what they do is immoral but not illegal).