Who Shot Olivia?

General Hospital: Anna tells Olivia that she wants to make her squirm. Olivia begs Anna not to kill her. Julian knocks on the door and Olivia tussles with Anna and the gun. Julian runs out to the balcony to try and get in the room and finds Cheryl. They struggle and the gun goes off. Duke, Robert & Sean hear gun shots and enter the room to find Anna standing over the body.