LARGO — This is what the world saw:

An emergency medical technician from Kansas who lived with his mother in a tidy brick house, where he helped her care for a 14-year-old boy.

A stay-at-home dad who lived with his wife in California and built a jungle gym next to his home for the couple's two adopted children, 6 and 8.

A puppeteer in Florida who performed in community centers, schools and churches and hosted kids-only pizza parties every Wednesday in his mobile home.

Bruce Foucart, the special agent in charge of Homeland Security Investigations in Boston, saw something else.

Over the past three months, the three men were arrested on charges that they produced, distributed or possessed child pornography. They were targets of a federal investigation that has reached 10 states and seven countries. To date, authorities have arrested 43 people, including 13 in the United States, and saved more than 140 children from further exploitation.

The youngest victim was 19 days old.

The accusations against many of the suspects are heinous. They include the rape of their relatives or their friends' children.

But for Foucart, who has investigated hundreds of pedophiles during his 27-year career, the online conversations among the men — the EMT, Michael Arnett; the stay-at-home dad, Jason Scarcello; the puppeteer, Ronald William Brown — made him sick.

He saw in these men, and their words, a deeper shade of darkness.

For months, according to court records, the three had discussed with each other sexual desires to kidnap, slaughter, cook and eat children.

Arnett bragged of the boys and girls he had murdered and roasted, according to the records. He took photos of a toddler posed in a pan inside an oven, authorities say; he was found with images of decapitated children that a medical doctor believed to be real.

To see a child cooked, investigators say Scarcello once wrote, "would be a dream come true."

Brown knew the boy he wanted to eat, says a federal complaint. They both attended the Gulf Coast Church in Largo. In one chat, according to the document, Brown said he wanted to either suffocate or strangle the child before he ate him.

Authorities won't say whether they believe any of the men have actually carried out their homicidal obsessions, but Susan L. McCormick of Homeland Security Investigations in Tampa said her agents are aggressively pursuing leads.

The investigators hope, like Brown insisted at his arrest, that it was all just fantasy.

• • •

The National Center for Missing and Exploited Children runs a program that catalogs child pornography to help law enforcement identify victims.

Since 2002, the agency has reviewed 72 million images.

That's about one photograph for every kid in America.

It's unknown how many men in the United States or the world possess child pornography, but the number is large and seems to be swelling.

The typical child pornographer, according to the center, is single and white and male. He could be any age. He is normally well respected in his community. He often works in a position of trust, like a pastor, teacher or coach.

His victims are seldom strangers. They are his neighbors' kids, his nieces and nephews or, often, his own children.

These men exist behind anonymous usernames in a sordid online underworld hidden from public view.

Still, they find each other, often through primitive software known as Internet Relay Chat, which allows participants to create public forums.

Since its creation in the 1980s, chat room topics have been diverse. Offerings are as benign as knitting and as disturbing as pedophilia.

Because the system is unregulated, users often make no effort to hide their interests, according to Neil O'Callaghan of the federal Cyber Crimes Center. He knew of one forum titled: "Rape, torture and murder children."

The men use code words. Young boys, for instance, are referred to as "asparagus." New contacts typically invite each other to a private chat on mainstream sites like Yahoo or Hotmail.

Within online communities, hierarchies form. The people who produce the most heinous images are given access to the most desired content.

"They try to one-up each other," Foucart said. "It almost becomes competitive."

• • •

The investigation now known as Operation Holitna started with a man just outside Boston who sent a photograph to an undercover federal agent.

In November 2010, Robert A. Diduca was arrested, and among his 10,000 images investigators found one that would begin to unravel an international web of pedophiles.

It depicted another man, a young boy and a toy rabbit.

The rabbit, federal agents discovered, had not been made in America. It was Dutch, and it led authorities to one of the most prolific child abusers in history.

Robert Mikelsons, a day-care worker and professional babysitter in the Netherlands, was convicted in May of abusing 67 children. Newspapers dubbed him the "Monster of Riga."

He was sentenced to 18 years in prison.

From those two men and their computers, investigators uncovered thousands of images and chat histories that led to dozens of arrests around the world.

Arnett, the EMT, was apprehended in May.

His computer pointed investigators to Scarcello and Brown. Then, last week, authorities arrested a man in Massachusetts who had corresponded for years with Arnett and Brown.

His arrest, authorities say, will likely lead to others.

"There's no end to it," Foucart said. "We just keep peeling back the onion, but that onion just keeps getting bigger."

• • •

When Brown was arrested last month, reports say, he admitted that he possessed child pornography, but insisted he was incapable of ever hurting anyone.

Prosecutors didn't believe him. They charged Brown with conspiring to kidnap the boy over whom he so long obsessed.

Viewers of child pornography often draw a distinction between themselves and child molesters. Members of the former group argue that they're only interested in pictures.

A 2008 study conducted by Michael Bourke, a psychologist for the U.S. Marshals Service, offered compelling evidence to the contrary.

He found that people who view child pornography also tend to sexually abuse children.

Bourke examined 155 prison inmates who had been convicted of possessing or distributing child pornography. Of those, only 26 percent had a known history of abusing kids.

Bourke observed the group progress through months of therapy and eventually found that 131 of those men — 85 percent — acknowledged that they had molested a child.

On average, each man had more than 13 victims.

Repeated exposure to child pornography makes abuse more likely, Bourke found, because it dehumanizes children. The online communities exacerbate the problem because they provide social validation and a sense of belonging.

Child pornography, the study found, is simply a part of the child molester's lifestyle.

• • •

Experts don't agree on how a pedophile becomes a pedophile.

Some argue that they're born that way. Others try to link the behavior to a traumatic event, usually abuse, in the person's childhood.

Arnett, Scarcello and Brown, according to authorities, were not simply pedophiles.

While it would seem even more difficult to determine what makes a person fetishize the murder and cannibalization of children, that question may not be impossible to answer.

Dr. Park Dietz is among the world's most prominent forensic psychiatrists. He has examined more than 20 sexual serial killers including Jeffrey Dahmer, who ate many of his 17 male victims.

Pedophilic cannibalism is incredibly rare, Dietz said, but he is certain the desire is learned, not innate.

More and more often, he said, fiction links violence with sex. Slasher films, for instance, often show an image of a nude woman seconds before she is murdered.

"That's how something previously unsexy," he said, "gets sexy."

And that blending can have a permanent impact on a man's mind.

Dietz once interviewed Joel Rifkin, who was believed to have murdered 17 women, mostly prostitutes.

Rifkin, Dietz said, had long been obsessed with a scene from the Alfred Hitchcock movie Frenzy, in which a beautiful woman is sitting in a chair just prior to being strangled.

"I think originally he was interested in her legs or chest, but he grew to think the strangulation was sexy," Dietz said. "And then he went out and did it."

Without examining Arnett or Scarcello or Brown, Dietz wouldn't know if they were capable of enacting the crimes authorities say the men had so many times imagined.

Such deviance, he said, requires a specific type of person who can ignore strict social norms.

"If you had someone with a recurrent sexual fantasy who was also a psychopath," he said, "nothing would stop them."

John Woodrow Cox can be reached at jcox@tampabay.com.