Green Mouse didn't say it out loud. He still chose to stay loyal to Noah's Ark, of course, but in Li Yifei's eyes, Green Mouse probably felt he'd already done too many things that went against the Heavenly Path, that heaven wouldn't tolerate him, that early death or late death, he had to die anyway. So Li Yifei simply followed Green Mouse's wish and killed him.
Anyway, people like this... one less alive is one less scourge. With that thought, Li Yifei felt a lot lighter.
After taking care of Green Mouse, Li Yifei searched the room and actually found some documents—information on the three experimental drugs. These were the things that hadn't had time to be moved or destroyed, and Li Yifei just happened to show up.
It was also thanks to him not resting and coming straight in, otherwise these documents would have been destroyed too.
