宿州市
After Emperor Xianzong died in 820 and was succeeded by his son Emperor Muzong, Niu Sengru was promoted to "Kubu Langzhong" (), a supervisorial official at the ministry of defense (戶部, "Bingbu"), and was put in charge of drafting imperial edicts. Later that year, he was made deputy chief imperial censor (御史中丞, "Yushi Zhongcheng"). At that time, there was a backlog of criminal cases in the prefectures, causing many people to be unduly detained while waiting adjudication. Niu worked to unclog the backlog, and indicted many responsible officials, causing the popular sentiment to respect him. In 821, when Li Zhichen () the prefect of Su Prefecture (宿州, in modern Suzhou, Anhui) was accused of corruption and sentenced to death, powerful eunuchs received Li Zhichen's bribes and spoke on his behalf. Emperor Muzong thus commented to Niu, "Li Zhichen is talented, and should be pitied." Niu responded, in advocating for Li Zhichen's death: