How Lyle and Erik could have invented a better story about what happened the night of the murders
Lyle, Erik, Jose, and Kitty were the only people to witness the events inside the Menendez house on August 20, 1989. By the next day, Lyle and Erik were the only two still alive who could give an account of what happened. And yet, they present a story that is far from likely to get them acquitted of murder and get them either convicted of manslaughter or acquitted on grounds of self-defense. They do this despite the fact that there is no one alive who can contradict them about what was said the night they killed their parents, and despite the fact that the shotguns were never found. They have years to come up with a better story with more details in their favor, and they never do.
Here are five pretty simple ways they could have done it.
Have Jose or Kitty find the shotguns, and call Lyle and Erik into the room
Trial lawyers like to talk about "bad facts" - facts that are not helpful to their side of the case and are helpful to the other side instead. One of the "bad facts" in the Menendez case is that Lyle and Erik entered the family room carrying shotguns. If you're Lyle and Erik and you're making up a story to save yourself from the gas chamber, why keep that "bad fact" at all? Why not say something like...
"We bought the shotguns for protection, and then when we brought them back home, we hid them in [place]. On the night of the twentieth, our dad yelled for us to come to the family room, so we did. He was sitting on the couch with our mom, and the shotguns were on the table. 'Boys,' our dad said. He sounded angrier than we'd ever heard him. 'Where did these come from, and why the fuck were they in [place]?'"
You've made Jose the person who got the guns out in the first place, and made him the reason why Lyle and Erik are in the room. The bad fact is no longer part of your version of events. Plus, you've made Jose be angry as hell, giving Lyle and Erik a reason to be afraid.
Say you picked up the guns only to keep them away from your parents - or, alternatively, say one or both parents reached for the guns
"I was afraid he might try to shoot us, so I grabbed both shotguns and handed one to Erik."
Alternatively:
"My dad/my mom lunged at the shotguns, and I yelled. I grabbed both of them and handed one to Erik."
Continue.
"'Dad,' I said, 'I love you. I don't want to hurt you. But what you're doing to Erik has to stop. We're going to go upstairs and pack, and then we're leaving here and we're not coming back.'"
Extra "points" for adding an attempt to leave the house.
Have Jose and Kitty say things that one, are enraging, and two, emphasize that Lyle and Erik have no chance of escape
Present Jose and Kitty as really escalating the volatility of the situation. "My mom looked at Lyle, and then suddenly she laughed this weird, choked-out sort of laugh. 'You think you're leaving here and not coming back?' she said. 'No, Lyle, you're not. You two are staying right here until your father and I say you can leave.'
"My dad started shouting, 'Leave and do what? Live on your own? You two won't last a week in the real world. You'll turn up on our doorstep begging to move back in.' Then all of a sudden he stopped shouting and looked at us. 'Lyle,' he said quietly, 'this is the last time I'll say this. It's none of your business what I do with my son.'" Maybe have him get really explicit - 'it's none of your business if I want to' X, Y, or Z, with X, Y, and Z being various sex acts or ways to hurt Erik. "'There is nowhere you two can go where I can't find you.'"
Emphasize an imminent threat of sexual violence, and portray Kitty as having explicitly condoned it
"My dad looked away from me and looked right at Erik. 'Now,' he said, 'you two are going to put those guns down. And then Erik is coming upstairs with me.' And my mom said, 'Do as your father says.'"
Have Kitty grab a shotgun after the first shot is fired
Example. "[Lyle or Erik] shot our dad, and our mom screamed. She grabbed [Lyle or Erik's] shotgun and tried to pull it away from him, and [Erik or Lyle] shot her." Detract from the prosecution's portrayal of Kitty as this meek battered woman, and turn her into someone who's trying to seize a shotgun that will make her an active physical threat to her sons. Remember, the shotguns have never been recovered, so as far as anyone knows, Kitty's fingerprints are all over one.
There is no physical evidence that contradicts anything in this story. It makes Jose and Kitty into clear and imminent threats to their sons' safety, and has them say things that are so incendiary that a reasonable person might shoot them without taking time to think about it. (One of the classic manslaughter scenarios is of a person who witnesses something enraging, "sees red," and kills another person without having time to think about it. Law professors like to teach this with the example of a man who comes home early from work, finds his best friend in bed with his wife, immediately grabs the gun on top of the dresser, and shoots them both dead before he's had time to premeditate the act.) It's not a perfect story. It can't be a perfect story, because you can't erase the evidence that someone reloaded one of the guns to shoot Kitty further times.
But it's a hell of a lot better than, "After Lyle confronted our dad, we kept getting these weird vibes from our parents. When they shut a door, we figured they were going to kill us, so we grabbed shotguns, entered the room, and shot them to death." If Lyle and Erik's account of the night of the murders is a made-up story designed to save them from execution, it's a feeble effort. (And definitely not what you'd expect from an aspiring screenwriter like Erik.)
The prosecution maintained that Lyle and Erik crafted highly detailed false stories of years of sexual abuse. All that time creating a sexual abuse narrative, and not even a few hours to come up with a better story about the night of the murders? Nope. They're telling the truth about what happened the night of the murders, because anyone with an average IQ and a will to live could invent a better story more likely to keep them out of the gas chamber.