So the guy really was chasing after someone with a dead body tied on him? The corpse looked like it weighed around 60-70 kg. Now Imagine running while having a 60 kg weight strapped on your body. At the very least, he would've looked a little bit sluggish even if you take the poncho into account.
He also had to do something regarding the corpse's legs. Unless the guy was actually much taller than the victim, the victim's legs would be sticking out under the poncho. If he just tied up the legs in a folded position, rigor mortis would've set and that would make the corpse look rather unnatural after he threw it towards Shinra.