Suspect 1: Rose Quartz

Motive: Earth's Liberation

As the leader of the Rebellion, Rose Quartz turned on her own diamond and fought to not only free gems that have been oppressed by their own society, but to also save the planet Earth from being assimilated into Homeworld's ruling. Shattering Pink Diamond would have benefited all of those endeavors.

Fact: All listed above is true.

Counter: All listed above is circumstantial and doesn't prove Rose did the deed.

Fact: There was an eye witness to the shattering.

Counter: Said witness has proven to be easy to fool with simple shape shifting.

Fact: Rose's reputation during the war makes her the prime suspect.

Counter: Said reputation makes her easiest to frame.

Means: Sword/Breaking Point/Pink's Own Power

There are at least three possible ways Rose could have shattered Pink's gem. Her sword, which was her signature weapon in the war. The Breaking Point, which was specifically designed to shatter any kind of gem. Throwing Pink's power back at her by deflecting it with the sword.

Fact: Witnesses say that Rose used her sword to shatter Pink Diamond.

Counter: Bismuth created the sword and made it specifically to be able to poof a gem's physical form without touching the gem itself.

Fact: Rose knew of the breaking point and its ability to shatter any gem.

Counter: The Breaking Point was stored away in a chest in Bismuth's forge and the Forge itself can't be opened without Bismuth whom was bubbled during the climax of the war.

Fact: Rose had a training room where a pre-programmed machine would hurl energy balls at her and said energy could be deflected and rebound by her sword. The same could have been done with Pink Diamond during their final battle.

Counter: None of the witnesses heard a fight break out nor was an explosion ever mentioned.

Opportunity: ?

Thanks to Blue Zircon, we know that Pink Diamond was attacked just outside her palanquin while she was on Earth. She stopped, or was made to/asked to stop, out in the open, existed a few feet from her palanquin, and was attacked from the front. We were given several key facts about the conditions of the event, but were left with even more questions.

Fact: Rose Quartz were a recognized threat for several hundred years

Fact: There were no Rose Quartz in Pink's court and guard.

Fact: All other Rose Quartz were bubbled and imprisoned.

Question: How did Rose get near her to begin with? Being literally the only Rose Quartz walking around freely would have made it next to impossible for her to get close to Pink without resistance.

Question: If she is guilty, could she have used another weapon? Another sword? Having a Bismuth in her army would have given her access to countless other physical weapons.

Question: If she did it, did she even need a weapon? As a quartz soldier, Rose is powerful even without a physical weapon and was seen taking down other quartz soldiers without any weapon on hand.

Question: Where were Pink's attendants? A diamond is never alone. Even when away from their court, their Pearl is always with them.

Question: Why didn't Pink's Sapphires' see the attack coming? Beings that can foresee the future should have instructed the guard on where and when to expect an enemy attack.

Question: Why didn't Pink's Agates fought off the threat? Even if Rose did over power them, they would have bought Pink enough time to escape unharmed.

Question: Why didn't Pink's Pearl cried out in warning? Pearl's are suppose to be utterly devoted to their diamonds/gems.

Question: Was Pink alone when she was attacked? It would explain why no one saw Rose approach Pink.

Question: When would she ever have been left alone? There doesn't seem to be a time with a diamond is ever truly alone with no other gem around.

Was it an inside job? Only someone who was already close to Pink would have had the opportunity to do the deed.

Who wanted Pink shattered? Besides Rose, if she wanted to, there may have, and in Bismuth's case, were others that wanted Pink gone.

Why was Pink shattered? Nothing in gem society is done without a reason. If Rose did it, it was because it was the only way to end the war and free the Earth. If it was someone else, it was because of their own motives.

In conclusion, Rose Quartz certainly had the Motive for shattering Pink Diamond and she definitely did had the Means available to her at the time. However, she didn't seem to have the opportunity needed to execute the crime. At least, not alone. Every fact that was found had a counter argument that provided reasonable doubt. This does not by any means proves that she's above suspicions, but it does not prove her innocence either. Only time will tell for sure if our sweet Rose had any thorns to her.