He apparently killed Sasori's parents in battle.
Later on, Sakumo and his team was given a top-secret mission during a war. During that mission, his team was captured. Instead of completing the mission, he went back to save his comrades' lives. Due to this Konoha suffered a huge loss and everyone hated him, even his own teammates. Sakumo fell into a deep depression and ultimately killed himself.
Recently, as Kakashi was walking to the afterlife after his battle with Pein, Sakumo stopped him and the two started talking next to a bonfire. After Negato revived Kakashi, Saskumo told him that he can now rest in piece knowing that his son has forgiven him and can't way to see his wife.