"He was such a nice boy. I never expected him to do this." Nobody will say that of Fuuma. "He was such a nice boy. A shame he died like that." This is what they must say instead.
Everybody must remember him as a warm gentle boy, because if he wins, nobody will remember him. They won't be around to remember anything.
So Fuuma, regardless, will be remembered kindly, while Kamui will be "a pity" or "that anti-social freak."
If he dies, they won't notice.
If he lives, he'll be arrested for the murder of Monou Fuuma.
You can't win.