Depending on the viewpoint, it is uncertain whether or not Nagahira intended to betray Yoriyoshi (the facts are unknown but judging from the context of the story), but it can be said that Nagahira's death was caused by Yoriyoshi's suspicion.
見方によっては、永衡に反逆の意図があったかどうかは（事実は不明だが、物語の文脈としては）不明であって、頼義の猜疑心が永衡を討たせたともいえる。