Against death penalty court cases?

I'm doing a CBA on the death penalty and if I'm pro or against. I've decided to be against because of my beliefs. Part of the CBA is to find a court case the we can right about that backs up what we believe. Does anyone know of any court cases for the death penalty that were unfair or a court case of someone who was executed and then found guilty after being killed? Links would be wonderful. :) thank you