'Walking Tall' sheriff likely murdered his wife in 1967, Tennessee officials say

[ProfessorGAC]

13. I Know The Test

And, I certainly won't argue that is not a high precision test.
It's also very technique sensitive, so operator to operator variation is quite poor.
But, we didn't know all that in 1975. So, that wouldn't have been an excuse to not initiate a full investigation based on the results.
The techniques used today didn't exist, or were their infancy in 1975. So, that test was still widely used 50 years ago.
All your information is correct. It doesn't explain the lack of legal action back then.
BTW: the test would have worked on facial wounds because both of them would have been hit with close range shots. But, the bigger point is that, back then, this was still the accepted test