Does one sit shiva for someone he killed?

Question

I understand sitting shiva to be an expression of bereavement. If I (hypothetically) was the victim of constant abuse which lasted for years and I ultimately, in an act of self defense, had to kill my abuser (a close family member) would I still be expected to sit shiva and be constrained by other displays of aveilut? I wanted the person to be dead so I would think that mourning would be inappropriate -- I'd be celebrating having escaped the abusive situation and saving my own life.

Would a pro forma shiva/aveilut be required regardless of the logic, propriety or sincerity behind the situation? While I can understand that there might be a sense of loss to the community or some metaphysical sadness because this person has lost the chance to do tshuva and return to his people, I as the victim would not want to mourn the loss necessarily.

Does aveilut/shiva have to go along with a sadness or does it stand on its own as a requirement regardless? Would a cold blooded murderer of a family member have to sit shiva (I understand the dissonance between being willing to take a life and still feeling bound by other halachot, but there are Jewish criminals who keep kosher in prison, so...)[any help in tagging would be appreciated..I can't find a tag for self-defense]

Answer 1

Yehoshua 6:26 - Yehoshua curses that whoever rebuilds Jericho should bury all his children - from the oldest when he starts to the youngest when he completes it.

ארור האיש אשר יבנה את העיר את יריחו. בבכורו ייסדנה ובצעירו יציב דלתיה

In Melachim 1 16:34 Chial Bais Ha'Aili rebuilds Yesricho and gets punished as per Yehoshuas curse.

Metzudas David Melachim 1 17:1 says that Achav & Eliyahu went to be Menachem Chial Bais Ha'Aili upon the death of his children.

From this you can see that if a father does something wrong and his child clearly dies for his sins, the father would still sit Shiva.

Answer 2

Your initial understanding is incorrect: sitting shiva isn't an expression of bereavement. Even though the two usually come hand in hand, being happy about the death--for whatever reason--doesn't make one exempt from the laws of shiva.

In other words, it's a question of halacha, and halacha in general isn't about your state of mind. If you're happy on the 9th of Av, does that make you exempt from fasting? No, of course not. If you're sad or in mourning on Shabbat, does that make you exempt from the laws of Shabbat? No, of course not.

So obviously the same applies here.