The jury after inspecting the place in question and after hearing the testimony, shall deliver to the justice holding such inquest its written signed verdict in which it shall find and certify how and in what manner such fire happened or was attempted, and all the circumstances attending the same, and who are guilty thereof, and in what manner. If such a jury is unable to so ascertain, it shall find and certify accordingly.
Tex. Code Crim. Proc. § 50.03