Had their mental ages been taken in court everything would've been proven in the brother's favor because no normal teenager, with loving parents, and a fuckton of money would have the mental age of a 10-year-old when their actual age is 20/18.

Had their actual circumstance (fear of getting murdered) been taken seriously, they would've had the option to look into Putative Self Defense (a mistaken belief that one life's in danger, so they use self-defense, where there's no ground for justification of said self-defense.)

Putative Self-defense could be with reasonable and unreasonable mistakes.

Reasonable Mistake: If the person’s belief in the need to defend themselves was reasonable but mistaken, they might avoid criminal liability altogether or face reduced charges. This could lead to an acquittal or a conviction for manslaughter (instead of murder) under the theory of imperfect self-defense, which reduces a murder charge to voluntary manslaughter.

Unreasonable Mistake: If the belief in the need for self-defense was found to be unreasonable, the person could still face criminal charges. The most likely result would be a conviction for voluntary manslaughter, rather than murder, as their actions lacked the intent required for murder but still involved recklessness or negligence.

Had the opposing council looked into the facts properly, the Menendez brothers would've walked free, or face charges of voluntary manslaughter, and only go to prison for 11 years, not life without parole...