There is a vast difference between using someone's curiosities to believe they are guilty of a crime, and investigating the individuals involved with a potential crime to see if one existed.

That is, if they had just picked up the joining of everyone that had searched for the details of child death in a car with those that had had a child death, that would be different. In this case, they had suspicions already, and are stitching together details from computer history as well as cell records and such.

This is all to say, when potential crimes happen, I personally think investigating them is not a terrible thing. Instant vilification is, but that is a different topic all together. Same for basically fishing for reasons of suspicion.