Salute!
A sad finding, but not one I dismissed back last year.
The debris field and the "witness" that saw the plane very low a minute before gave me the clue.
I was in the system when USAF decided that we had to make our stateside low altitude nav "legal". So we let down to lower than 500 feet AGL and practiced. Being in the VietNam group, we flew as low as required to get the job done whether a CSAR or CAS or interdiction mission. Then we came home and had restrictions. That all changed about 1974, and we trained to fly lower and lower. It worked.
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I have a hard time with a "nugget" IP that does not have a lotta hours in tactical planes serving as an instructor.
RIP.