White Diamond in the title card, Yellow Diamond destabilizing the Zircons after BZ says only another Diamond or someone with their authority could've shattered PD. Maybe White and Yellow conspired against Pink, wherein Yellow sent White to Earth to do the deed, then got rid of or corrupted White to leave no evidence?
(I actually thought it was Pink Diamond in the title card because that whole thing is so pink and this is all about PD’s death, but yeah it actually is White Diamond since you can see her forehead glowing)
Anyway, it is entirely possible that it was Yellow Diamond. The main reason to suspect that she didn’t do it though it because it would be too obvious. Her actions such as how ready she was to rush through the trial and how fixated she is on destroying earth could easily be explained by her having actually done it. However, one big thing that says otherwise is the fact that she let Rose (Steven) speak at all. YD has no way or knowing that Rose and Steven aren’t actually the same person. If Rose really didn’t actually shatter PD (and we’re still not 100% sure that she didn’t, but obviously there’s more to what happened) then Rose could absolutely testify otherwise (from the DIamonds’ perspective that is). So the fact that YD let Steven speak at all indicates her innocence more than anything else, I would imagine. But again, it’s still not impossible.
As for White Diamond, I imagine one of two things. Either she is so far above the other Diamonds that she doesn’t even feel the need to involve herself in the trial of Pink Diamond’s murderer, or she’s simply very far away doing war stuff or whatever and wasn’t able to make it back in time for the trial (since it happened on such short notice). But given the perceived power hierarchy, I doubt that Yellow Diamond could have destroyed White Diamond, and I doubt just as much that she could have totally covered it up, even from Blue Diamond
