However, I ran the description of Vassallo's death through an online translator, and found that it does not support your lurid account of Vassallo and Bernardi being burnt alive.
This is the translation of what the link says:
This seems to me a much more plausible account, since there is no reason why the Germans would have wanted to kill Vassallo and Bernardi in a far more brutal and sadistic way than the other villagers, who were simply shot. The motive of wanting to make the two bodies disappear in the rubble of the burning house is entirely plausible, and is sufficient to explain why the two men were taken to that particular house, which was already on fire.The two ambassadors are sent down to Piazza Italia and dragged into the yard of the home of the photographer Ramero. The house is already burning. They are hit more times with rifle butts, killed, sprinkled with petrol, and set on fire. The aim is clear; they want to make the bodies disappear with the rubble of the house. But the vault of the corridor resists and acts as a shield.
The state of Vassallo's body indicates that it had been exposed to very high temperatures over a prolonged period, eg in a house fire, causing a cremation effect. The bodies of persons who have committed suicide by setting fire to themselves with an accelerant are never as badly burnt as this, since most of the heat is directed outwards and the accelerant is quickly consumed; they are nearly always fully recognisable with only the skin being burnt.
It seems to me that the tale of Vassallo and Bernardi being burnt alive is a fabrication designed to make the German perpetrators appear far more brutal and sadistic than they actually were.