He didn't do it out of choice. He didn't kill her with the first shot so he had to leave her to either bleed to death or survive to tell the story..............I don't don't think he had MUCH by way of choice.
Agreed. He had NO choice. What was he supposed to do, take her to hospital and admit it because she didn't die with the first shot. No, he had to shoot her again - stage the suicide - stage the phone call and follow through with his plan.
Yes, he had the choice not to stage suicide.
Leaving it open to interpretation as to what happened? A burgular breaks into the farmhouse and slaughters the family, including kids in their beds? BAMBER was the last one to see them all alive, of course he would of come under immediate suspicion and he wouldn't have the phone call to place him away from the scene.