I highly recommend the book "An Exorcist Tells His Story" by Fr. Gabriel Amorth. I just finished posting links to it over at the Harry Potter thread. This book is not at all sensationalistic. It is very down-to-earth, yet you will be utterly convinced of the reality of demonic spirits and their influence on many people's lives. The book is solidly theological, not a recounting of gruesome incidents.
Here is a web page dedicated to the book:
http://www.catholic-exorcism.org/pages/book-story/story-home.html
Fr. Amorth details the horrendous scandal in the present-day Church, including in Rome itself, in which the reality of evil is denied at the same time that occult influence is skyrocketing. This incident in NY just confirms his observations.
I also read his book and found it to be very informative. I often wonder with all the so-called "mental illness" running rampant these days if in some cases it is just some form of possession. So many people don't want to believe that evil does truly exist and possession by evil demons is certainly possible.
St. Michael watch over us all!