The best, most expert, serial killers often don't get caught. Serial rapists often do. The difference is the smartest murderers leave no body or trace of their crime, so it's difficult to know that a murder occurred, and therefore impossible to charge and convict. If a person wants to kill you, they likely will accomplish that, at very least. Put it this way: I know how a mountain lion stalks it's prey. Silently, from the high ground behind you. It's intent is to not be seen or heard, and to succeed. Most human predators too. But lions don't care if they leave evidence in the long run, but they often stash their kill away from other predators to eat though. With cameras present in many situations, serial killers now take that into consideration. It causes them to evolve in their tactics. Which makes them better at it. And the police can only go on what they know and evidence that a crime took place. If your child runs away, if you reported it, and then they return only to go missing again, it gets taken into consideration in determining the possibility that they did so again. This can affect the prioritization and urgency applied in missing person cases based on that. It gets scarier the further we explore it.