1 Peter 3:9
9 Not rendering evil for evil, or railing for railing: but contrariwise blessing; knowing that ye are thereunto called, that ye should inherit a blessing.
It does not matter what someone dies to you. It does not matter how despicable someone is to you. You can never repay there evil deeds with evil deeds. As a Christian, getting even should not be something you think of doing. It does not matter if you do something in the name of getting even, an evil act is still just that, an evil act.