Sure, I would and I would expect them to cover for my murders. Isn't that is what family is for?

Ths strikes me as being the natural order of things. It's her job to protect you. It's not your job to protect her.

I'd die for my child. I'd do almost anything for her, including perjure myself (unless she was quite obviously going to be a menace to herself or others if released) but I don't expect her to do the same for me.

That is basically it for me as well. Sure, I would lie to protect any close family member but I wouldn't let myself get in much trouble unless it is one of of my children then all bets are off. I am a big fan of sociobiology. I am younger than my parents and have kids of my own so we fall in ever increasing importance in the hierarchy in descending birth order. I expect my children and grandchildren to feel the same way.

I'm always amazed when family members reflexively defend someone accused of a heinous crime. "They would never do that! They wouldn't hurt a fly!" I know all of my family members, and they are great people. AS FAR AS I KNOW. And that is key. No one is an open book, and everyone is capable of everything. If my mother turns up dead and my father is implicated as the killer, I'm not automatically think there's a mistake and rush to his defense. And vice versa.

I think a key sticking point is that people are imagining up their own scenarios and how they would respond to it and the universe of possible crimes is large. If one of your parents killed your other parent, you have a true conflict and I can see how you would want the justice system to do whatever is necessary because that is family-on-family crime. I wouldn't cover up for a serial sex offender either especially if I had a high degree of confidence it was actually true.

I imagined the scenario as a murder that was a one-off kind of deal and had some good reason behind it. Maybe it was a person that kept threatening your sister's family including their very lives but the authorities wouldn't take it seriously. One night your sister believed the threat was about to become real and did something about it. It is murder by the strict definition of the law and would be prosecuted as such but only if there are enough witnesses to make a good case. Your sister confessed to you that she did it and even told you where the body was buried. You can talk or not talk. The choice is yours. Right now, it is just a missing person's case and may stay that way.