Living and working in isolation in his father's one-bedroom flat in the corner of Dublin's Mountjoy Square, Eric Eoin Marques allegedly became the biggest dealer of child abuse images in the world.

According to US law enforcement, the 28-year-old US-born Irishman was one of the most important men on the "Darknet" -- a protected sub-layer of the internet inaccessible to normal search engines that enables people to conduct illicit activities.

A report in the Irish Independent describes him as quiet and unassuming, "a loner who struggled to mix and complete his schooling ... the perfect neighbour in his anonymous block of 16 flats – never causing problems, never playing loud music, and so quiet playing computer games in his flat that people never knew he was there."

An unnamed neighbor told the paper: “There was something odd about him. I had friends who lived with me for a short period who also said that he was a bit strange. Most of the people here you’d see going out shopping or getting their mail, but never Eric.”

Marques was arrested three weeks ago on a warrant that includes charges of distributing and promoting child pornography on the internet.

US authorities are reportedly seeking his extradition on charges of distributing, conspiring to distribute, and advertising child pornography. It was further alleged that he aided and abetted a conspiracy to advertise child pornography. If convicted, he faces sentences of up to 30 years in prison.

It is believed Marques hosted 550 servers in Europe and allegedly ran Freedom Hosting, an infrastructure that allowed sites to operate anonymously -- including child-abuse sites, money-laundering operations and encrypted mail systems and fraud forms. For allegedly supplying the infrastructure to allow these sites to work, he may have earned thousands  a month. However, whether Marques knew of the content of these sites remains yet unknown.

In response to a question about adult porn, Marques posted on a chatroom, "“We don’t have any rules about… content or links as long as it’s legal.”

Marques' father, Antonio, a Brazilian-born architect who worked for the Irish Rail for 15 years and now lives in the United Arab Emirates, maintains that his son is innocent and was not personally involved in collecting the images, which include the rape and torture of children.

“He doesn’t allow it," said his father, who acknowledged that illegal material had been discovered on sites hosted by his son’s company.

“There is something bad in there, but it is nothing to do with him.”

“If I rent out an apartment and somebody does a crime in it, am I to be prosecuted?” he said.

According to the Independent, Marques displayed few signs of his wealth and rarely socialized.

“He seemed like a nice guy. He was, as his father said, not keen on mixing with a lot of people,” said Jasmin Prnjavorac, a former colleague of Marques' father. “He was just a quiet kind of guy, doing his own thing. I wouldn’t say he even had too many friends. Maybe he had a few, but that’s what I got from his father.

“He [Antonio] was concerned about Eric because he didn’t finish school, he was concerned about his future, he was saying he was in his own world and quiet; not talking about much even what he was doing at home.”

Said one neighbor, “He was very bland. Everything about him was bland and quiet.”

Marques was born in New York. His parents are divorced, and he lived with his Irish mother and sister and visited his father on the weekends. In 2005, father and son set up Ultra Hosting, a business which included web hosting, domain registration, design, marketing and consultancy services. The Independent reports that the last accounts, which were lodged in November 2011, did not show signs of economic activity, though Eric Marques admitted in court that he was earning substantial sums.

According to US law enforcement, Marques has been conspiring to distribute child abuse images since 2008.

Marques, who is next due to appear in court on September 11, has been refused bail although his lawyers have indicated they will continue to seek bail.

Said Dublin city councillor Christy Burke, whose constituency includes Mountjoy Square, “I was absolutely appalled. If this guy gets bail and goes back, I will march on his house like we used to do with drug dealers and ‘Out! Out! Out!’ He’s not welcome in my constituency,” he said. “The FBI don’t make those statements for nothing. The sooner he goes over there, the better.”

According to the Independent, Marques' arrest is significant and represents a large strike by global law enforcement against operators of the underground internet and illegal multi-billion-dollar industries such as drugs, arms and porn.