What happened to Lupin? In Episode 3, after Death the Kid makes his appearance in front of Lupin, Kid "senses" Patty is off center and thus the formation is no longer symmetrical. As he complains about it to Liz, Patty watches Lupin escape though the manhole.

Now Lupin had a huge sack of Human Souls with him when he escaped, which is obviously a bad thing since devouring human souls allows one to gain power quicker but leads one down the path of being a Kishin. This would be something that can't be ignored by Death or the Overseeing Death Scythes.

So I am wondering, is it ever explained what happened to Lupin and the souls he stole after he escaped from Kid?
This is quite a downer of an answer, however there really is nothing more.

After escaping, within neither the anime nor manga, is Lupin mentioned again. I personally read Soul Eater and watched it, I don't recall any more sign of him, and this 'thesis' is backed up by the wiki:


  Debuts - 
  Manga - 'Death the Kid', 
  Anime - The Perfect Boy. Death the Kid’s Magnificent Mission?


As you can probably assume, this is indeed Episode 3, which I trust is the appearance you are referring to (being his only). It mustn't have ended with such a bad fate, as the use of the human souls, as we probably would have heard about a new Kishin being born.

I doubt it, as I'm not following it, however there is a possibility his name is at least mentioned in Soul-eater Not!, however I have yet to hear anything regarding that.