when Mussolini was captured, the war was over. the fascisti had collapsed and there was no risk of him falling into enemy hands, so no circumstances that made immediate execution a necessity. forcing him to stand trial & make a pathetic display of himself in court could've easily been as beneficial as an execution, if not more in the long run. the Reds running a public trial of fascist leaders could've been a serious political tool, and execution very well could've followed that anyway. it unironically was a miscalculation from the PCI to forfeit a piece for the post-war settlement like that.

for displaying the corpse, it's a bit medieval i guess, but the main error was allowing retribution-ist justice rule instead of realpolitic.