How can we make sure that assault charges are filed?

My boyfriend was assaulted and worked and called the police. The police took his statement on two separate occasions and they knew who they guy who assault him was. The police report says that no charges were filed and that no statements were taken. In their report, the police claim that they could not find the guy. His work wants to know why no charges were filed and why no statements were given, although they were. How can we correct this situation and attain some sort of justice?