Come the fuck on. Poor woman has come to terms in her own limited way with the senseless loss of a child several decades ago, with very little closure.
Simple enough, it was a random attack by a drifter. They came to town, saw the opportunity, cased the place, and then carried it out. They left and never came back. Despite what CBS crime solving shows are pointedly calculated to convince you as fact, it's still pretty hard to solve a random murder case without personal ties involved. This is why serial killers can sometimes kill for decades without being caught. They select their victims largely randomly, tied to their particular kink. It's even more difficult when it's not a sexual attack, which tend to involve preferences of the killer, and it's just a money grab.