Hard to tell. The picture was widely used in the media, and they're usually quite careful about that kind of thing. There's something reddish in it, but it could be material from the truck or its contents. One of the photos the police released of his guns had some red foamy material in it, another photo had some stringy red material (plastic?) lying in the road, and there were various red items in the bed too. I'll mark it NSFW just in case.