The Mr. Jimmy Earl Burt who says in Dec 1963 that he saw the shooter turn off into the alley just after the shooting, and that he saw this from his vantage point at the intersection of Tenth and Patton, is saying something that Mr. Bill Brown doesn't like. Therefore he is an UNREAL witness.
However, the Mr. Jimmy Earl Burt who in 1968 doesn't mention his having seen the shooter turn off into the alley just after the shooting, from his vantage point at the intersection of Tenth and Patton, is not saying something that Mr. Bill Brown doesn't like. Therefore he is a REAL witness.
Now some would characterize this approach to evidence as shameless cherry-picking. Not me. I see it as an example of Mr. Bill Brown's rigorous and powerfully simple methodology for arriving at conclusions that will be palatable to Mr. Bill Brown.