The fact they happened 40 years ago doesn’t make them any less brutal. The fact that most people don’t remember them or weren’t alive at the time does not justify doing this.
He has served forty years and, according to the article posted above on this thread, he “is incarcerated in a Tennessee Special Needs Facility.” That means he is either disabled, dying or, at best, or extremely sick. So releasing him on parole is not going to endanger the public, and is going to save the taxpayers a boatload of money in providing him free medical care.