Clue
Spoiler:
I believe its Anakin in the Chancellor's office with a lightsaber. I think Anakin easily kills Windu thus startling the remaining Jedi as to how powerful Anakin has become. Palpatine and Windu are arguing over Palp's decreeing himself Emperor, Windu leaves and is met by Anakin who says "I've come for you 'Master' Windu" Windu pulls his saber and after a few moments Anakin does the Ronco Dice-a-matic on him. When Obi Wan and Anakin are fighting I could see something along the lines of Obi Wan swinging at Anakin, cuts a rock in half and high pressure steam from the volcano shoots out onto Anakin scalding and stunning him. Obi Wan then jump kicks him over the edge into the steam and lava and assumes he's dead. oops.