Te Waotu School Board of Trustees employment subcommittee chair Megan Ranger talks about the impact of child pornography allegations against the school's principal Bruce Darroch.

When police knocked on the door to tell a mother her son may have been sexually abused - she lied.

"I didn't tell my child at the time."

She didn't want her son to know the truth. Bruce Darroch was his principal at Te Waotu School in Putaruru. When police knocked on her door in August 2014, he had been arrested after the largest bust involving child sexual abuse websites in the United States.

Former Te Waotu School prinicpal Bruce Darroch was found guilty of child sexual abuse offences.

Darroch had shared photos of her son - and other children - at the school over the internet with paedophiles.

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After a three-day trial in the Rotorua District Court, Darroch was found guilty of three charges on Tuesday, March 15.

Former principal of Te Waotu School, and convicted peadophile Bruce Darroch.

He was convicted of possessing objectionable material, making an objectionable publication and on two charges of failing to assist police with a search.

He was found not guilty of two other charges of supplying objectionable material.

During his trial, the court was told that the phots of the students Darroch shared were not of them being sexually abused.

Supplied Vittorio Francesco Gonzalez-Castillo, the American peadophile whose arrest led New Zealand Police to Bruce Darroch.

But this did nothing ease the raw anguish of the parents as details of his offending emerged. They detailed Darroch's online chats and stories he shared with other paedophiles where their children became characters in his twisted fantasies.

"My child said he's ruined and tainted their school years. We sent our children there thinking they were safe," the mother said.

For the first time, the full story of Darroch's arrest and conviction can be told. It is one that spans law enforcement agencies across the globe and is one of more than 300 separate investigations worldwide.

It's a story that begins a decade ago.

In May 2006US law enforcement agencies launched Project Safe Childhood, a nationwide initiative to combat child sexual exploitation.

A specialist operation as part of this initiative targeting a child exploitation website, Operation Round Table, was about to claim its first New Zealand conviction.

Speaking for the first time about the case to New Zealand media, US Immigrant and Customs Enforcement (ICE) deputy director Daniel Ragsdale, said it was one of the largest online child exploitation investigations in its history.

So far, investigators have identified victims in the US, United Kingdom, Canada, Australia, Belgium and New Zealand.

The underground website, a hidden service board on the Tor network, operated for about a year from June 2012 to June 2013 and contained more than 2000 videos. Its membership topped 27,000.

It was the arrest in Arizona on January 24, 2014 of one of the websites administrators, Vittorio Francesco Gonzalez-Castillo, that set the wheels in motion for the arrest and subsequent conviction of Darroch.

It was to this man Darroch sent photos of his students and shared his twisted fantasies.

Gonzalez-Castillo is serving a 30-year prison sentence in the US after pleading guilty to distribution, possession and production of child pornography.

The Federal Bureau of Investigation (FBI) described his offending as "large-scale trading and distribution of graphic and sadistic child pornography".

At his sentencing in the US, Carin Duryee​, lawyer for the US Attorneys Office, outlined his role as an online mentor for fellow paedophiles.

"Other child molesters benefited from this defendants advice on how to encrypt, how to avoid detection, what not to do and what to do, and that included conversations about how to get a kid, how to drug a kid, how to groom a kid."

Gonzalez-Castillo provided US authorities with the password to his computer - something Darroch failed to do with New Zealand Police - and among his files was one called "lustboys KWB".

The file contained chat logs and most damningly of all, photos and videos police discovered had been taken in New Zealand.

The photos and videos were sent to the police's Online Child Exploitation Across New Zealand (OCEANZ) unit, from where they were forwarded to police school liaison officers.

One of them, former Tokoroa police constable Ann Samuel, was also the Te Waotu School community officer at the time.

She saw the photos. She knew the kids.

"I know his parents personally, I know him well," she said in court. "In all the photos, I recognised faces of other pupils too."

Samuel's evidence prompted the Crown to make a key claim at Darroch's trial - that Darroch and the man known online as "lustboys KWB" were the same man.

It was a claim given weight by Darroch in his own words, when the court was shown the DVD of his interview with Detective Sergeant Trevor Brown.

Brown read Darroch excerpts from the conversation between Darroch and Gonzalez-Castillo - who Darroch knew online as "Administrator B".

In one online chat, in which he referred to a video clip of a boy at his school taken in his car, Darroch told Gonzalez-Castillo that when the boy said "I've been a bad boy," he became aroused.

He referred to one child as "another bondage boy" and said he believed the child would be "great in bed".

He also admitted to Brown that he used a particular online service because of its anonymity.

Darroch denied, however, that he had any physical contact with young boys, though he admitted in light of the online conversation it was a "logical" question.

"That's just getting caught up in the chat," he said.

"That means nothing in reality. You just get swept away ... as embarrassing as this is, it's just a matter of getting caught up in the chat."

Evidence was also given by Customs officer and forensic electronic investigator Bruce Ellis, who took part in the search of Darroch's home on August 26, 2014.

He said a number of hard drives, laptops, Apple devices and USB sticks were recovered, most of which were encrypted.

"[They are] impossible to read without that password. If we tried using our forensic tools, we'd see gobbledygook."

Deleted data was recovered from one USB however, found at Darroch's school office.

It contained images featuring children involved in sexual activities.

Darroch also referred to these images in his police interview when questioned by the leader of the OCEANZ unit, Detective Senior Sergeant John Michael.

"Would you acknowledge those images are unlawful," said Michael.

"Yes ... I have to accept those have been found," said Darroch.

He was also asked about the photos of school pupils he had sent to Gonzalez-Castillo.

"Do you think the parents of these boys would think you've exploited them?" he was asked.

"Yes, I do," Darroch replied.

Judge Tony Snell described the stories, which featured pupils at Darroch's school, as "graphic, detailed and with sustained rape fantasies".

"[The stories had] clear personal knowledge of the boys. The main character, a teacher, that is you."

When told police would be interviewing the boys in the photos, Darroch was adamant he had never abused anyone.

"I know you probably hear that a lot," he said. "I can look you in the eye and tell you I have never abused a child."

Snell was convinced, however, that Darroch was the man known online as "lustboys KWB".

"[You] clearly knew what child porn was," he said.

Darroch was remanded on bail to an address in Napier until sentencing on June 24.

There is one person, however, who won't be attending the sentencing. The mother who lied to her son to protect him.

She fears Darroch may escape prison a prison sentence.

"I'm quite prepared for that. I don't think I'll be going to the sentencing."

The US connection

It was an unusual name on the charge sheet for now-convicted New Zealand paedophile Bruce Darroch. Vittorio Francesco Gonzalez-Castillo.

It was to this Arizona man that Darroch was initially charged with supplying child exploitation images, and the transcript of his sentencing reveals the true horror of the man Darroch associated with on the 'dark web.'

Gonzalez-Castillo is serving 30 years without parole in a US prison.

"Other child molesters benefited from this defendants advice on how to encrypt, how to avoid detection, what not to do and what to do, and that included conversations about how to get a kid, how to drug a kid, how to groom a kid."

That was the description of Gonzalez-Castillo from Carin Duryee​, lawyer for the US Attorneys Office at his sentencing.

According to Duryee, Gonzalez-Castillo believed using an online, virtual world was harmless.

"Of course that didn't explain why there were children in diapers or toddlers being raped. It didn't explain the sadism, it didn't explain why he chose a community of [online] child molesters."

Remarkably, Duryee said Gonzalez-Castillo continued to offend even as he knew the net was closing in.

"He continued to offend, in more than one way and both in New York and in Louisiana, after the search warrant was executed and while knowing there was an indictment pending, though he hasn't yet been arrested," she said.

"Because this is a needs-driven behaviour, these offenders find it very difficult to stop."

Gonzalez-Castillo didn't restrict his offending to online either, as his own half brother confirmed in a victim impact letter read to the court.

"That Winter very radically changed my life, as it was that Winter that I was raped by the man who I held in such high respect, my brother."

"Learning that your brother is involved in the biggest child pornography ring in history and that you are part of it is like a hole to the head," he said.

"He betrayed me on a level no one should ever experience."

A second impact letter from the mother of one of the exploitation ring victims described the anxiety, fear, anger and depression suffered by her daughter.

"She says there isn't a day I don't wake up with an ache in the pit of my stomach."

Even Gonzalez-Castillo's father, Victorio​ Gonzalez, condemned his sons actions.

"You deserve to be punished. The hurt you've imparted on others is immeasurable."

Judge Raner​ C Collins told Gonzalez-Castillo that if he had opted for a trial instead of a plea deal and a 30-year sentence, he may well have been jailed for the rest of his natural life.

"This case just blows my mind. I thought I'd seen the worst case ever about six months ago, and you've topped that in spades."

He said the 30-year sentence offered Gonzalez-Castillo the chance for something of a life upon his release, but he had a warning too.

"If you do anything wrong once you get out, you'll be back in prison so quick it'll make your head swim."