smerel- I am not sure you are correct about any of it. If he was poisoned, someone would know and I doubt there would not have been a doctor involved. And if it was molestation, I still don’t know that you are right about it getting any more serious attention. Unfortunate but true.
As a possible answer I will tell you that historically, people don’t get molested once, there is a process of emotional abuse beforehand in the grooming of the victim, and there is rarely only one victim (unless it is a parent and his own child). People around the child will notice differences in them and their behavior, drastic changes that they all notice, without understanding what happened. And there is plenty to work with in the details of how he groomed the victim, how he got them to the place, who knew they were there etc. It is usually much more elaborate, involved and traceable than just pouring someone a drink. And often there was an adult who was told and chose to ignore it. They will be another link.
So I agree that if it was like that (someone sneaks up on a kid, molests them once and disappears into the sunset) it would probably have little chance of being brought to justice.
Hope that helps.