How was the murderer caught?

The reader spends the grand majority of Alice Sebold's The Lovely Bones waiting for justice to finally catch up to Mr. Harvey, the middle-aged sexual predator who brutally rapes and kills Susie Salmon, the narrator. Unfortunately, that particular reckoning never occurs. Near the end of the book, it appears that Mr. Harvey has not only gotten away with his crimes but also is about to add another victim to his list. However, while the authorities never catch up to him, the world finds a way to deliver justice. The last the reader sees of Mr. Harvey is as he is stalking yet another girl near the end of the book. He emerges from a Greyhound bus and goes into a diner. Shortly after, a teenage girl who had been on the bus comes in. Susie, the narrator, states,

It was a teenage girl who had sat a few rows ahead of him for the last few hours, playing her Walkman and humming along with the songs. He sat at the counter until she was done using the bathroom, and then he followed her out.
I watched him trail her in the dirty snow along the side of the diner and out to the back of the bus station, where she would be out of the wind for a smoke. While she stood there, he joined her. She wasn't even startled. He was another boring old man in bad clothes.
He calculated his business in his mind. The snow and cold. The pitched ravine that dropped off immediately in front of them. The blind woods on the other side. And he engaged her in conversation.
"Long ride," he said.
She looked at him at first as if she couldn't believe he was talking to her.
"Um hmmm," she said.
"Are you traveling alone?"

At this point, it seems that Mr. Harvey is planning on taking the girl into the woods, assaulting and killing her, and leaving her body in the woods. He is attempting to determine if anybody would notice she is missing, as Susie makes an observation:

It was then that I noticed them, hanging above their heads in a long and plentiful row. Icicles.
The girl put out her cigarette on the heel of her shoe and turned to go.
"Creep," she said, and walked fast.
A moment later, the icicle fell. The heavy coldness of it threw him off balance just enough for him to stumble and pitch forward. It would be weeks before the snow in the ravine melted enough to uncover him.

Mr. Harvey falls down the ravine and dies from either the fall or the injuries he sustained. His body isn't discovered for weeks. So, while he is never caught, arrested, and put on trial for his terrible crimes, the world has found a way to make sure he never hurts anyone again.