Or, if you prefer: p(Q|P) > p(Q) => p(¬Q|¬P) > p(¬Q)
Wait, I can phrase that better. OP said that this verdict is evidence of bias. Responder says conservation of probability means that, if the not-guilty verdict is evidence of bias, a guilty verdict must be evidence against, which is illogical. "Illogical" is a correct characterization of this use of probability.
Examples:
1) I am biased against Ms. Pao, and she wins: "This just goes to show that women can sue for anything these days, and win millions!"
2) I am biased against Ms. Pao and she loses: "See, women will sue you for discrimination even if you didn't do anything wrong!"
3) I am biased in favor of Ms. Pao and she wins: "See? This is clear proof that the bias against women goes all the way to the top of Silicon Valley!"
4) I am biased in favor of Ms. Pao and she loses: "See, this is proof that businesses can discriminate against women and not suffer any consequences."
Given that, in order for me to take someone's claim seriously, I would want them to pre-commit - before the result is announced - to a "court outcome interpretation." I don't care whether that interpretation is "regardless of what happens, the court outcome is irrelevant" or "I will accept the court ruling as 100% true and correct" - I just want consistency.
But that's not really the sense in which an outcome in Pao's favour would've been used dialectically.
Rather, people currently disagree in their assessment as to how probable it is that there is institutional bias. Those who are very confident that there is institutional bias feel that others, who are skeptical of the existence of institutional bias, are mis-assessing the existing evidence.
And so, yes, were an outcome in Pao's favour to come down, those who are currently confident that there is bias would use this to bolster their argument that the weight of evidence is on their side, such that others should revise their probabilities upwards to match. But even if an outcome in Pao's disfavour came down, they would still consider others to have mis-assessed the existing evidence, and would still feel the correct thing for bias-skeptics to do would be to revise their probabilities of institutional bias upwards, albeit perhaps not as much. And there would be nothing irrational or illogical in this.
[In the same way, if I were to argue with someone who claimed to have found an algorithm which could compress arbitrary data, and I challenged them to compress and restore a particular file, and they failed that challenge, I would say "See? You couldn't do it; that should convince you that your claim is erroneous". But if they happened to pass that one particular challenge? I wouldn't say "Ah, ok, you should feel even more confident in your claim to have found perfect compression". I would say "Ah, that challenge happened not to add to my evidence against your claim, but I still have good reason to disbelieve your claim, your claim is still false, and you should still sharply revise your credence in that claim downwards to match mine."]