define "worst case of online exploitation"

In this case, the feds found over 200,000 child porn images on a man's computer. Six hundred of the images were of particularly vile crimes.

The Fremont Tribune says, 

“In numbers of images alone, this was the worst case of online child exploitation discovered by our investigators,” said Nebraska Attorney General Jon Bruning. “Coupled with the young age of the victims, it’s difficult to put into words the horror of this case. We appreciate U.S. Attorney Gilg’s office for its cooperation and expert prosecution that brought Mr. Sheldon to justice.”

 The worst case of online child exploitation? Really? Does this mean that law enforcement hasn't caught any of the evil people who actually abused those children or took the photos and videos? Because, to me, finding the people responsible for sexual abuse of children would be much worse than finding someone who collected photos and videos. Yes, even if the collection included many truly nasty images.

 "The horror of this case" seems to be a bit confused. Isn't the horror of this case the discovery that someone did something horrible to the children in the images? As far as I can tell, this man hasn't been accused of touching anyone.

Gilg expressed her appreciation to Bruning’s office for referring their investigation for federal prosecution. Gilg noted the mandatory minimum sentences and the sentencing guidelines for child pornography crimes makes the federal courts a favorable venue for prosecuting the most egregious child pornography offenders.

Yes, those mandatory minimum sentences and sentencing guidelines certainly are a stroke of luck for prosecutors.