Destroying Angel

An entire family is murdered during a bizarre home intrusion in a quiet, middle class neighborhood in southern Utah. All members of the household are found hanged in the garage, their wrists bound, mouths taped, nooses strung over the ceiling joists. Neatly lettered on the wall in marking pen are the words:
FOR AND ON THE BEHALF OF DUDLEY LEAVITT, WHO IS DEAD.

But then, less than a week later another household is found murdered, with the same cryptic message but mentioning a different pioneer ancestor. A few days later there is another. And then another, and another...
FOR AND ON THE BEHALF OF WILLIAM H. DAME...ISAAC HAIGHT... JOHN M. HIGBY... NEPHI JOHNSON...

Someone was systematically killing by vicarious execution the descended families of the perpetrators of the Mountain Meadows Massacre.