I believe he was initially hit by the National of Islam assailant’s car and then essentially pushed some distance into the barricade. So, it’s easy to see how he could have multiple head injuries, both front and back.
Many of the barriers that they use around the Capitol are the kind that ‘pop-up’ as a barrier of last resort; they look like a backwards ski-ramp with the leading edge designed to essentially slice into whatever vehicle is trying to pass. He was trapped between one of those barriers and the car. It had to be absolutely gruesome which might explain why they’re not very detailed in the description.
There are a fair share of ghouls on FR. they want every little detail, along with diagrams and photos.
It doesn’t take a genius to look at the scene and figure out what happened.