Looks like he was laid on his back over a log in water. His head and legs would have been under the surface and would not decompose nearly as fast as the parts exposed to air.
Stuffed ass first into an empty oildrum, then acid poured in, or piranhas...
You can't get out, you cant drown yourself, you're just stuck there dying slowly .....I've done it many times when I worked for the...shhhh..... can't say any more.......