Sorry but your just seeing what you want to see. 

Go to .31 of the video and you'll notice your blood smear magically disappears even though the contrast should be greater against the white of the car seat. 

Now if its a seat belt it makes sense that it disappears from view as the camera pans right the pillar slowly blocks more of the view of the interior as the angle of the camera changes.  

I understand some folks just need someone to hate but physics and facts must not be ignored when judging such a serious matter.

Also can you give me a definitive definition of "pretty definitively"?