but because of the torture before, and dissection, freezing and burning of her body after the act.

Well, in Germany Graumsamkeit/cruelty is a murder attribute as well, so I'm indeed. and it seems to work similarly in Italy. But as always it's the intend that matters. I.e. you need to want to make your victim suffer. If you're merely bad at killing people that won't be held against you. I'm not quite sure why the judges didn't find cruelty, but the articles I can find appear to be all machine translated so I'm not sure how much actually was done while the perpetrator believed his victim to be alive. Keep in mind that the court needs to prove intend here. That's easy if the perpetrator prepared the crime by buying a lot of acid or a poison that is know to cause suffering, but for hands-on crimes it's hard.

Anything done do a dead boy is negligible here. Dead bodies can't suffer and are pretty much just things legally. Not treating them with dignity is illegal, but it's not a serious crime at all.