In Massachusetts (at least) your employer is required by law to run a background check on you before you are allowed to work with children in any capacity, paid or volunteer. That means working as a teacher, camp counsellor, school janitor, school bus driver, etc.

But background checks can only provide so much information. If a person has no criminal past, their background chack will come up clean. Just because thay have a clean background check doesn't mean that they're not the scum of the Earth, either.

It would be interesting to know if this guy had a history of any kind.

I'm not trying to sound insensitive (believe me, this is a terrible tragedy, and I have to deal with perverted sickos like this all the time) but if his record was clear, what more could the police do?

Let's flip the situation:

Someone applies to be a janitor at a school. He has been laid off/sacked/whatever. His criminal check is completely clean, but because he's working near kids, the police are constantly checking up on him. Suppose his intentions were good and true? Haven't his rights been violated?