What if the Public Security Bureau doesn't file a case?

Hello, my parents were chopped by three unidentified people at home during the National Day in 2009. My father probably got revenge because he offended others at work. My father is in charge of dams in the town and belongs to Shuyang Water Resources Department. Because it is not allowed to mine yellow sand near the dam for reselling, Zhang in the town has been offended. Zhang found someone to cut my parents in the middle of the National Day in 2009. At that time, he was taken to the hospital and was seriously injured. My parents immediately reported the case, and the police in Shuyang County also filed a case for investigation. All the materials are in the public security bureau. In the past two years, my father has been asking for a statement. However, from the county public security bureau to the municipal public security bureau, and then to the people's government, we have not yet got a statement. The criminal police team has been deliberately delaying, as if Zhang was looking for someone to find a relationship. I want to ask, do you want justice, or do you want to go to court directly? Thank you very much