Saxophone lost by high school, how should I proceed now?

Hello everyone,

I need advice and suggestions on how to proceed with my son's missing the alto saxophone due to the school's negligence. My son is in the marching band and all the students in the band were asked to keep their musical instruments in the truck as they were going for an event. My son kept his saxophone in the school's truck but found it missing when they reached the place of event. We have been emailing the band teacher asking for updates but the teacher instead of replying to our emails directly is sending messages through our son. Is this attitude acceptable? The band teacher is refusing to file a police complaint and told my son that since the missing saxophone is our property, the complaint should be filed by us. I am confused about how should I proceed further to solve this situation. Should I involve the principal and counselor?