李德裕
Late in 831, Li Deyu reported that Xidamou (), the Tufan officer in charge of Wei Prefecture (維州, in modern Ngawa Tibetan and Qiang Autonomous Prefecture, Sichuan), surrendered Wei Prefecture, which Tufan had captured from Tang decades earlier, to him. Li Deyu advocated accepting the surrender and using Wei Prefecture as a launch pad for a major campaign against Tufan. Niu opposed, arguing that this was a violation of the peace treaty between Tang and Tufan and that, should a war start, Tufan forces could reach Chang'an easily. Emperor Wenzong accepted his argument and ordered that Li Deyu return Wei Prefecture, as well as Xidamou and his soldiers, to Tufan. Tufan had Xidamou and his soldiers massacred. The massacre brought much popular sentiment against Niu, and was commonly viewed at the time to be the result of the conflict between Niu/Li Zongmin and Li Deyu. It was said that this incident caused Li Deyu to resent Niu even more.