At minimum, there should be physical evidence.
If any contact occurred, it was him hitting her or it was purely accidental.
My Sister knew her well and says that she was a sweet 59 year old Grandmother.
Not the type to be ramming complete strangers at 1:30am, on a country road, while alone.
From the story, it sounds like the witnesses were passengers in the murderer's vehicle.
See post #22.