I have never seen a piston failure like that before.  I would recommend sending the failed parts to a metallurgical lab for analysis. They can probably tell you conclusively if the failure was a result of fatigue, stress, environmental attack or material defect.  

It looks like these pictures were taken just as the piston was being extracted from the cylinder. But, there are no piston rings or rider band evident on the piston.  Were these parts removed and then the scene restaged?  Or, were these parts destroyed in a fire resulting from the failure?
 

Johnny Pellin

thanks JJPellin for your comments
yes we plan to send a sample to a third party lab. to specify the problem.
you are right, theoe pictures were taken just as the piston was being extracted from the cylinder.
in one of the photos and under the feet of the persons you can see the rubber rings which weren't damage at all.
and luckly there were no fire or explosion took place at the scene.
thanks again for ur passover