There seems to be an increasing interest among many people about Angels  I read a book many years ago that was very well researched and written entitled Angels: Elect and Evil by C. Fred Dickason.  He covers just about any topic you can imagine when it comes to both good and bad angels.  There is a great deal of scripture in this book to back up each of his points.  I don't consider myself to be an expert on this topic, but if things like this interest you, this book is worth a read.  It really helped me to understand more about Angels.