Emperor Gaozong died in 683 and was succeeded by his son
Li Zhe the
Crown Prince (as Emperor Zhongzong), but Emperor Gaozong's powerful wife
Empress Wu retained ruling powers as
empress dowager and
regent. In 684, when Emperor Zhongzong displayed signs of independence, she deposed him and replaced him with his younger brother
Li Dan the Prince of Yu (as Emperor Ruizong), but thereafter wielded power even more firmly. She soon faced a rebellion against her led by
Li Jingye the Duke of Ying, but quickly defeated the rebellion. However, Li Jingye's rebellion caused Empress Dowager Wu to suspect many people of opposing her, and she began to encourage secret reports. Zhou had been serving as a low-level secretary (尚書都事,
Shangshu Dushi) at the executive bureau of government (尚書省,
Shangshu Sheng), and he became involved in serving as a secret police official for her, eventually promoted by her to be deputy minister of justice (秋官侍郎,
Qiuguan Shilang). It was said that Zhou was involved in the deaths of thousands. In 688, there was a false accusation by a slave of the official Hao Xiangxian () against Hao, whose deceased grandfather
Hao Chujun had previously served as chancellor during Emperor Gaozong's reign and had opposed Emperor Gaozong's one-time plan, during his time of illness, to have Empress Wu serve as his regent. Empress Dowager Wu still bore grudges against Hao Chujun for that episode and took this opportunity to have Zhou investigate Hao Xiangxian. Zhou found Hao Xiangxian guilty and sentenced his entire family to death. (On the way to the execution field, Hao Xiangxian tried to flee and also loudly yelled out insults against Empress Dowager Wu and accusations that she was committing immoral acts; he was eventually killed by the guards, but as a result of what Hao Xiangxian did, thereafter until her death, whenever prisoners were to be executed, their mouths would be stuffed with wood so that they would not be able to yell out insults.) Later in 688, in the aftermath of another failed rebellion, led by Emperor Gaozong's brother
Li Zhen the Prince of Yue and Li Zhen's son
Li Chong the Prince of Langye, Empress Dowager Wu considered wiping out the senior members of the imperial Li clan, and she put Zhou in charge of the plan. Zhou thereafter arrested Emperor Gaozong's uncles Li Yuanjia () the Prince of Han and Li Lingkui () the Prince of Lu, Li Yuanjia's son Li Zhuan () the Duke of Huang, and Emperor Gaozong's aunt Princess Changle and her husband Zhao Gui (), brought them to the eastern capital
Luoyang, and forced them to commit suicide. He then further massacred the princes' family and friends. In 689, still bearing grudges against Wei Xuantong, who was a friend of
Pei Yan, a chancellor that Empress Dowager Wu had executed in 684 on suspicions that he opposed her, Zhou falsely accused Wei of having said, "The empress dowager is old. It is better to support the emperor, for he will last longer." In anger, Empress Dowager Wu ordered Wei to commit suicide. Zhou also falsely accused the general
Heichi Changzhi the Duke of Yan of treason, and Heichi was strangled to death. In 690, Zhou suggested that the Li clan members be stripped of imperial clan status, and Empress Dowager Wu did so. He also falsely accused the chancellor
Wei Fangzhi, who was subsequently exiled and executed in exile. Then, at the instigation of Empress Dowager Wu's powerful nephew
Wu Chengsi, he accused Emperor Gaozong's sons by
concubines,
Li Shangjin () the Prince of Ze and
Li Sujie the Prince of Xu of treason. Li Sujie was strangled, while Li Shangjin committed suicide. Later in 690, Emperor Ruizong yielded the throne to Empress Dowager Wu, and she took the throne as "emperor" of a new Zhou dynasty, interrupting Tang dynasty. Yet later that year, the prefectural prefect Li Xingbao () and his brothers were falsely accused and sentenced to have their clan executed. A subordinate of Zhou's at the ministry of justice, Xu Yougong () tried to get the judgment reversed but was not able to. However, Zhou then accused Xu of acting on behalf of treasonous individuals and requested that Xu be executed. Wu Zetian refused to execute Xu, but for a time relieved Xu of his duties. == Death ==