Due to secretive and personal reasons, Jian Ruyun, ranked fourth on Liangwang Peak, had been cautious about Liu Shisui the entire time.
Back when Liu Shisui was interrogated by Shangde Peak, the Zuo Yi case was mentioned. More than ten years later, the case was mostly forgotten by a vast majority of people, though not by Jian Ruyun.
Through the connection he had in his clan, he found out that Zuo Yi had visited the Curtain Rollers before his death. Zuo Yi had an old friend among the Curtain Rollers, who was seemingly investigated by Shenmo Peak as well.
All this strengthened his determination to investigate the case further.
Because Jian Ruyun was worried that some people on the Green Mountain might cover up the clues for Shenmo Peak, he didn't tell anybody about his suspicions, and he intended to investigate the case all by himself.