Questions for the Canon | "Who Killed Ariana Dumbledore"

So, one question that forms in your mind after finishing Harry Potter and the Deathly Hallows is 'who killed Ariana Dumbledore?'
For those of you whose memories are a little clouded over, Ariana Dumbledore is the younger sister to Albus and Aberforth Dumbledore, and there is a mystery over who killed her(from a three-way duel): Albus, Aberforth, or Gellert Grindelwald.
I think that Albus Dumbledore is the one who killed Ariana Dumbledore.
One of the reasons I think this is because Albus was obviously a powerful wizard. He is the only one that Lord Voldemort ever feared. He is the master of the Elder Wand, and is the wisest Headmaster of Hogwarts.
Another reason I think this is because Albus was so worried about finding out who did kill Ariana. He was too caught up in his 'For the Greater Good' teenage world, that once Ariana was killed, he realized that it was completely possible that he could've killed her.
Ariana was trying to stop the duel between the three of the wizards. I think that Aberforth would be trying to hurt Grindelwald for basically tearing apart the Dumbledore family. Dumbledore would be trying to get Aberforth, to protect Grindelwald. Grindelwald would probably be shooting at Aberforth, just to defend himself. I think Ariana would jump in front of Albus, since Aberforth was her favorite brother, and she would try to help him, therefore Albus's curse would hit her instead of Aberforth.