A bombing? A gas explosion? it's too soon to tell but this footage is terrifying! Eye witnesses are saying the blast looked like it came from inside the building. What a tragic, tragic day. This is the U.S.A, not one of those embattled countries you see on the news nightly. That might sound harsh, but I think we're all a bit raw right now. Please use caution when viewing, some of these videos are graphic and may be difficult to watch.