Why did lawyer Chen surrender to save the suspect?

I realized that I had inadvertently helped the criminals escape the punishment of the law. According to the material of Douban film "Save the Suspect", lawyer Chen found many doubts during the investigation, which showed that Li Ming was not the real murderer, but the scapegoat. In the process of uncovering the truth of the case, he gradually realized that the case involved a complex conspiracy. With the deepening of the investigation, he realized that he should expose the truth and ensure justice. Therefore, he chose to surrender and take responsibility for his negligence or inaction in the investigation of the case. Saving the Suspect tells the story that Chen is a clever lawyer. One day, her daughter was kidnapped suddenly, and the kidnapper asked Chen not to plead guilty for a condemned man within five days, otherwise she would kill the ticket.