Special Case: Never Crossing the River of Forgetfulness

[Main suspense, slight supernatural elements, no cp, no emotional line, main plot direction] There are a series of serious cases in Jiangcheng City, each of which is vaguely related to a police scandal a few years ago... Is it the revenge of an innocent soul, or the return of an old friend? The truth is clear. If all the unwilling dead people can get the opportunity to return to the world to redress their grievances, will the darkness of this world really have nowhere to hide?