Henry Marshall was a USDA investigator who was closing in on Billy Sol Estes a friend of people in very high places.
It must have really borken his heart to learn that the President of the U.S. (LBJ) was very possibly engaged in criminal activities.
Mr. Marshall must have really, really wanted to commit suicide.
He finally succeeded by knocking himself unconscious, managing somehow to breath through a hose attached to the tailpipe of his pickup truck, and -- all else failing -- shot himself several times with a bolt-action rifle.
(Years later in the 1980s with new information our rulers said, well maybe it wasn't suicide.)
...and then he hovered from his car out into the woods, where he laid down and died. (There was no dirt on the bottom of his shoes.)