President Xi Jinping has appointed a special unit headed by a senior policeman and deputy minister of public security to investigate former Minister of Public Security Zhou Yongkang. Using police to investigate a former high-ranking Party member is a departure from the normal practice of subjecting Party members to "shuanggui" detention, an extralegal means of interrogating and disciplining Party members. Experts have cited the sensitivity of the case and Xi's desire to be seen as promoting the rule-of-law as the reason for conducting a formal police investigation.