It began when shocked investigators found video on a computer of a 2-year-old-boy being sexually abused. A forensic investigation of that computer in Milford, Mass., lead to a man related to the child in Arizona, and to a day-care worker in the Netherlands who posted the video on an international child porn website.

Two years later, tracking down the picture of that exploited little boy has resulted in 33 arrests worldwide, the rescue of 138 children, and the takedown of an international network of men bent on sexually exploiting children, according to federal officials.

The sprawling, complex investigation was capped off today, when Robert Diduca, the Milford man who had the image of the 2-year old boy on his computer, was sentenced to 18 years in prison. The Dutch day-care worker, Robert Mikelsons, was sentenced to 18 years in prison on May 21. The Arizona man, Brandon Keith Jones, was sentenced to 35 years in prison in March, after confessing to repeatedly sexually abusing his nephew, and two other children under the age of 6. The other suspects in the case, eight from the U.S., have either been sentenced, or are awaiting sentencing.

"Thanks to international cooperation and first class forensic analysis by Homeland Security Special agents here in Boston, along with our Massachusetts State Police partners, an individual arrest in Milford has led to a network of child pornographers that has spanned the globe," said Bruce M. Foucart, special agent in charge of Homeland Security Investigations, Boston. "An individual photo discovered on Mr. Diduca's computer has led to 33 arrests and 138 children being saved worldwide. Eight of those arrested live in the United States."

The way investigators from HSI busted the international ring reads like a detective thriller.

Investigators found the picture of the 2-year old boy, and thousands of child exploitation files on Diduca's computer. One file showed he had engaged in an online chat with Brandon Keith Jones in Mesa, Ariz. The subject of that chat was depraved and shocking, with Diduca trying to persuade Jones to sexually abuse a 4-year-old and take sexually explicit videos of the abuse. Diduca even provided the individual with a camera and suggested how the child should be posed. Investigators immediately called the Mesa police, who took Jones into custody, and removed his nephew, and other children, from a dangerous situation.

In addition, investigators found an astonishing 27,000 more child porn pictures on Diduca's computer. Many of those pictures did not appear to originate in the U.S. Working with Interpol and various national police agencies, investigators were able to determine the pictures came from the Netherlands.

Dutch media and police released edited versions of some of the photos and asked the public to help identify the children. A 2-year-old was identified, and that broke the case wide open. The child attended a day care center where Robert Mikelsons worked. Mickelson subsequently confessed to sexually abusing the child, and dozens of sex crimes, Dutch prosecutors say. He also was the webmaster for the child exploitation web site.

Dutch prosecutors said Mikelsons provided thousands of leads, resulting in 13 arrests in the Netherlands, eight in the U.S., six in Canada, four in Britain, and one each in Germany and Sweden. The child porn website that Mikelson ran has been taken down.

Officials say the investigation was part of Operation Predator, a nationwide HSI initiative to protect children from sexual predators, including those who travel overseas for sex with minors, Internet child pornographers, criminal alien sex offenders and child sex traffickers. HSI encourages the public to report suspected child predators and any suspicious activity through its toll-free hotline at 1-866-DHS-2-ICE or by completing its online tip form.