Brennan testified under oath that he saw Oswald firing a rifle from the sniper's nest that Oswald had left his prints in, that's true. I do believe him. That being said, I avoid using him in the case against Oswald. CTs love to bash him, as they do others who implicate Oswald's guilt in murder.
You're right, the CT's in their last desperate gasps are now left attacking any eyewitness who implicates Oswald.
But before anything was officially known, Brennan's first day description of Oswald, was broadcast on the Police radio within 15 minutes is worth repeating because the CT's have no answers, they say that Brennan's description can be half the population of Dallas which is just absurd because first of all half the population is women and then when it's further dissected we have slim, around 5 foot 10 height which crosses out another stack of the population and next we have an appearance of about 30 which Oswald with his thinning scalp is about right and finally we have him as being white.
So after eliminating a wide cross section of the male population of Dallas we are left with a relative handful of people and then out of the employees in the Depository this is reduced to a mere fraction.
So by logical deduction we are left with a tiny fraction of people and considering that Oswald owned the rifle and owned the relative fresh prints in the exact window that Brennan specified, we can pinpoint who did the shooting!
Now if Brennan's description was elderly, black, fat, very tall and completely bald then we can write off Oswald, but it wasn't.
JohnM