As stated, you should report it, that is no tool box, at least not for the kind weuse on a vehicle. The way the foam is cut out it looks to me like an instrument case, something like ground penetrating radar or X-ray used to check welds on a pipe line. Something along such lines. The air valve is for air transport,open it so that inside air pressure is stable at altitudes. That could be a very expensive case.
I'd use it for HAM gear, computer and video camera equipment case. If the cops don't know who owns it, you keep it and put it on Ebay, you can buy a tool box! If you do find the owner, I'm sure they will buy you a tool box! :Wow1: