It should be obvious that Yellow Diamond was involved in Pink’s assassination, but what you might have forgotten is that Rose could not have done the dirty work. If Pink was in fact shattered with a sword then Rose’s sword would have been useless since

Bismuth: “I designed this sword for a fair fight. It can cut through a Gem’s physical form in an instant! Destroying the body, but never the Gem.”

But you know who does have a sword that could shatter PD?

Pearl!

If Pearl was Pink Diamond’s, and still was when the shattering happened, she would have been able to approach undetected because she was supposed to be there. That wouldn’t be Pearl’s only qualification: as a Pearl, and a defective one at that, Pearl had no rights. Yellow Diamond could have her shattered on the spot and it wouldn’t have been worse that breaking her sister’s hair brush. Futhermore, if Pearl told Pink Diamond, she Pink wouldn’t believe a Pearl over her sister

If Yellow Diamond ordered her to shapeshift into Rose Quartz and kill Pink Diamond, she would have no choice. Of course, the minute Pearl realized she was the only loose end she would have been forced to flee anyways.

Everyone: “Pearl can’t shapeshift!”

Can’t she? We’ve seen Pearl change her outfit on screen before, and according to Peridot their clothing is just a part of their bodies. We’ve seen Pearl change her outfit, but she always comes up with an excuse when it comes to changing her form. What if the reason is that she vowed never to use it again after using it to kill her diamond and frame Rose

Despite all the speculation about Rose being evil or at least a sociopath, do we have any doubt that Rose would forgive Pearl on the spot? She was coerced into framing Rose for something Rose probably planned on anyway!

Rose would take responsibility for the assassination and for that act of kindness Pearl would devote herself to Rose on the spot.

Everyone: “But then why didn’t Pearl and Garnet tell Steven?”

When have the gems ever been honest with Steven? Do you really think Pearl would admit to her own son that SHE murdered someone in cold blood and then let his bio mom take the rap? For all we know, not even Garnet knew the truth!

So where does this leave us? Is this all speculation? No, look at the facts again

Yellow poofed her own lawyer to silence the truth

Pink was killed by a sword that cannot have been Rose’s

Someone Pink trusted must have killed her

Her Pearl did not warn her in advance

Pearl uses a sword despite her gem weapon being a spear

Pearl can shapeshift but makes up excuses not to

Pearl was the ideal assassin, because she was supposed to be there and easily coerced

Can there be any doubt that Pearl is our culprit?

I rest my case your honor