Why were "both friends and foes" invited to funerals as noted in the nonfiction book, Albion’s Seed: Four British Folkways in America?

The author noted that murder was so frequently the cause of death that "both friends and foes" were invited to funerals and were expected to touch the corpse. The reason being that if the murderer attended, the others might be able to figure out who it was by what happened when he touched the corpse of the victim in the presence of the victim's loved ones.