Angel of Darkness

I just finished reading The Angel of Darkness by Caleb Carr. It's the sequel to The Alienist, which I read over the summer and really enjoyed. The Angel of Darkness wasn't quite as good, but was still an interesting, fun to read mystery. All of the same characters from The Alienist are back in this book, but the author switches the narrator to a different character. I found myself wondering why he made that choice. Was it to challenge himself as a writer? To make the book a slightly less typical kind of sequel? It seemed to me the the story could have been told just as well from any of the characters' perspectives, including the original narrator from The Alienist. But that said, the new narrator didn't detract at all from my enjoyment of the story. Like the first book, my favorite part was still all of the historical descriptions of New York during that time.