It’s not vigilantism period. Forgiveness is not a legal issue in any case FWIW.
http://www.ktsm.com/news/sheriff-father-kills-man-sexually-abusing-his-daughter
“Asked whether they would press charges against the father, the sheriff responded, “You have a right to defend your daughter. He acted in defense of his third person. Once the investigation is completed we will submit it to the district attorney who then submits it to the grand jury, who will decide if they will indict him.”
http://www.victoriaadvocate.com/news/2012/jun/11/sl_beating_death_folo_061212_179174/
1. The grandfather has broken english, meaning the victim is of a minority group, most likely hispanic/Mexican.
2. The grandfather says the father is remorseful that the perp died because he did not mean to kill him.