If you could keep the body cold in a cooler with ice packs until Monday, you could take or send the body in to your state vet for a necropsy to look for what is going on. What state are you in? Here is a list of state vets to contact the one in your area:
https://www.metzerfarms.com/poultry-labs.html
https://www.metzerfarms.com/poultry-labs.html
