The still-widening investigation has been code-named Holitna, after a river in Alaska with many tributaries.

"They are the worst of the worst," said Bruce Foucart, agent in charge of the U.S. Customs and Immigration Enforcement agency's Homeland Security Investigations unit in Boston. "This isn't just a child that's nude and someone's taking pictures of him; this is a child that's being raped by an adult, which is horrific."

The case began to unfold when Robert Diduca, a Sheraton hotel manager from Massachusetts, sent the photo of the Dutch boy to an undercover federal agent in Boston. Diduca, a married father of three who used the screen name "Babytodd," thought he was sending the picture to another man with a sexual interest in babies and toddlers.