Actually, I have. I think the second part of the excerpt above demonstrates one of the reasons why forgiveness is so powerful. Letting the hateful act of another ruin the lives of you and your family is just handing a further victory to those who are evil.
Please don't misunderstand me; it is very painful and heartbreaking to lose a loved one, especially to murder. I'm not pretending that it doesn't hurt like hell. But inviting seething hatred into your heart and the hearts of your family is simply adding fuel to the fire and prolonging the pain. It does nothing to the criminal, except give some of them a perverse sense of satisfaction when they see it.
I've found peace through the plain truth: Murderers cannot be punished completely for their crime(s), no matter how horrible that punishment may be. What they have taken cannot be restored by the actions of men. Hating and wishing vengeance upon them accomplishes absolutely nothing. God knows all and is perfectly just. He will make certain it all evens out in the end.
I don't feel "seething hatred". I only want justice to be served. Part of closure is seeing the criminal receive his sentence. In my brother's case, it is still unsolved after all these years.