Eliminate Criminals

In 1995, in the city of Jixiong in northeastern China, two robbers wearing burlap sack masks killed many people and committed a robbery. Everyone at the scene was killed. The cruelty of the crime left the entire city in shock. The police station director ordered the criminal police captain, Zhang Jian, to investigate the case. Jiang Hongbing, who had retired from the martial arts world for many years, decided to team up with Captain Zhang Jian to avenge his fallen comrade. As a result of the killer's meticulousness, what difficulties will they face in tracking down the case, and how will they uncover the clues to solve it?