The 15-year-old boy who murdered Karen Aim, a backpacker in New Zealand, was sentenced last week. From The Guardian:

Aim's father Brian told the court he had looked forward to walking his daughter down the aisle on her wedding day but had instead found himself walking with her coffin.

Outside the court he said he felt sorry for Broughton.

"He has taken away Karen's life, but he has also destroyed his own. "If I go down the road of anger and revenge that would only destroy my life."

Asked what sentence he thought his daughter's killer deserved, he said it was not an issue for him, adding: "It's too late, Karen is dead."

For me, this - in so few words - says all about why the death penalty is wrong.