When I was a kid some asshole dumped their garbage bags along the road near my house. My dad opened the bag, found some discarded mail with the asshole's address, then called the police who contacted the man and told him to come remove his garbage, you know, NOW, as we are waiting here just filling out his summons to appear. Man came and took away his very ripe smelling garbage.
Perhaps this is best left to the professionals. You really don't want to open a bag with a dead body in it. Aside from the nightmare fuel, there are serious potential health risks as OGG pointed out. Call the cops and report it as a suspicious object. They will go all bats hit response wise, and probably arrest the fuck nut who tossed it.