Your Google-fu is weak; a search like http://www.google.com/search?num=100&q=%22J.K.%20Rowling%22%20%22Harry%20Potter%22%20death%20interview turns up Wikipedia linking to several interviews, and then some quick C-fs turn up:

Death is an extremely important theme throughout all seven books. I would say possibly the most important theme. If you are writing about Evil, which I am, and if you are writing about someone who is essentially a psychopath, you have a duty to show the real evil of taking human life.

http://www.accio-quote.org/articles/2001/1201-bbc-hpandme.htm