I'd begin by seeing whether the piston goes up and down when you rotate the crankshaft. You can do this by removing the spark plug and either looking in through the hole, or bending a piece of tie-wire to reach over toward the bore. At the top of the stroke the piston comes level with the top of the cylinder.
If the piston crown does not come up to the top of the bore, you can be sufficiently sure the connecting rod is broken.
If the piston goes up and down, you will need to take the cylinder head off to see whether the valves open and close.
If the rod broke while the engine was not running, it is fairly likely that it was terminally damaged earlier and just chose this moment to separate completely. That is a piece of luck, because the rod will probably not have damaged the internal parts. You may have no collateral damage other than perhaps a scored crank-pin (due to running without oil, if that is what caused the broken rod). As a rule of thumb, rods are broken either due to lack of oil, or by over-revving the engine. Over-revving usually doesn't damage the crankpin, but running dry probably will have.
