In The Lovely Bones, what behaviors could have given Mr. Harvey away, had they been discovered by others?

It's
rather telling that, even when his evidence of his strange behavior comes to light, Mr. Harvey
still gets away with his crimes. When Lindsey breaks into his house, she discovers a notebook in
which Harvey has sketched the underground structure of the cornfield where he murdered Susie. To
her, this is incontrovertible evidence that he's guilty as hell. Why else would he make such a
drawing? But Harvey explains away the sketch; drawing it was simply his way of coming to terms
with an appallingthat had affected him so deeply.

His...