I’m pretty sure it was the Flood. Before that, presumably Abel was tending animals for fur, to yoke plows to and most significantly to offer up as sacrifices.
The Catholic Church allows for the possibility of universal salvation, although belief in universal salvation is not widely held (for a notable exception, check out Julian of Norwich).
So yes, it’s possible that Hitler (and Stalin, and Pol Pot, and all the other dead villains you can think of) are in Heaven right now (or at least in Purgatory), and will rise from the dead at the end of the world.
It looks like I was right
From here http://www.aish.com/sp/ph/Vegetarianism_and_Historys_First_Murder.html