I've never read a post from a mod telling us to stop talking about the bloody shirt. And I've read most of every thread.
Tricia has overruled a previous rule, and it's now OK for us to discuss the people in the SW, initials only. RB was named in the SW. And the shirt WAS brought up by a reporter in the most recent press conference. So I see no reason why it can't be discussed.
With that said, I don't think RB had anything to do with MB's murder (but I don't rule it out). And I think the shirt has dog's blood.
BUT... A corroborated alibi can be flawed if the person corroborating it is in cahoots. So let's say that hypothetically the lab finds some stray hairs on that bloody shirt. Remember, they're going to be thorough and pick up ANYTHING they find on that shirt, not just the blood.
Now let's say that the lab tests the evidence from crime scene and finds hairs on a tool, MB's body, etc. And what if they find that the DNA matches the hair from the bloody shirt.
That gives them probable cause for a SW compelling anyone who touched that shirt to submit a DNA sample.
RB is not someone I'm actively looking at, any more than LE. Just laying out a hypothetical and pointing out why it's important to at least test that shirt and see what is found, even if the blood is truly dog blood.