Thing I don't understand is she felt the need to lock the bathroom door behind her - in the middle of the night? Seems a strange thing to do. My guess is they were rowing and he went at her with the cricket bat. She locked herself in the bog for protection. Not having any of that he went and got his 9mm to learn her a lesson.
We all saw what a nice bloke he was when that other bloke had the temerity to beat him in the Olympics. After years of his marketing machine convincing us that the blades give him no advantage suddenly another bloke with blades has got an unfair advantage??? But did you notice how quickly the machine got into action when they realised he was blowing it. He U-turned faster than a conservative politician.
Jealous angry bloke being told she doesn't want him anymore. Gets the bat, she runs into the bathroom for protection. Locked the door. He shoots through it.
Surly if he wanted to top her it would have been a lot easier to get a taxi driver to do it for him, say he was forced out of the taxi when they leveled a pistol at him, then they raped her and shot her.