In 1175, Sukechika, who found that out, drowned Sentsurumaru in the Matsu-kawa River for fear of invoking the wrath of Heike (the Taira family), and furthermore, he plotted to kill Yoritomo himself.
安元元年（1175年）、祐親はこれを知ると、平家の怒りを恐れ千鶴丸を松川に沈めて殺害、さらに頼朝自身の暗殺も図る。