I wanted his story to come full circle, because all that you really get of him in the first book is just a glimpse, and in the second book he appears to be nothing but a madman, except for subtle flashes of sanity. But I never really thought of him as a villain in the conventional sense. He's certainly not good, but he's not evil either. So in the third book, I wanted to show his better nature, the man underneath all the drug addiction and anger. I can understand that.
Villains are fun, and sometimes when they show their humane side they lose their luster.
On the other hand, there were readers who were aching to see Biagio's decent side, because they knew it was there all along. As for the story writing itself, I have to say that the third book was fairly easy to write because I knew what I wanted to accomplish. But it wasn't because the characters took over. I'm happy to say that almost never happens to me. The characters pretty much do what I tell them to do.