?KILLER IS DEAD? ?????? ?BGM? ? ??????:Q (
http://www.nicovideo.jp/watch/sm21504567) Found one of the songs uploaded on niconico, pretty epic indeed... it's listed as "Last Battle" so it might possibly be the theme for the final boss/level so be warned for people that might not want to be spoiled.
...Is the same song from the first trailer and it's the final battle theme. I hear it in a video/walkthrough. Is a very good track. I will keep searching the soundtrack