A university lecturer who blackmailed people he met online into sending him degrading photos including acts of paedophilia has been jailed for 32 years. Dr Matthew Falder's conviction is thought to be the first UK prosecution related to sadistic "hurtcore" material located on the dark web. It follows a four-year, worldwide investigation involving security services from the US, Australia, New Zealand, Israel and Europe.
Falder was, on the surface, a Cambridge-educated academic with a good job, family and friends.
His Twitter feed revealed a love of dinosaurs, baking, table-tennis and 3D-printing, featuring selfies, crossword puzzles and innocuous questions about how to "put nice quality videos online?"
Yet, behind the scenes, he operated under anonymous usernames on the dark web to share videos and images of paedophilia, blackmailing victims into sending him horrific material he would then pass on to other offenders.
The National Crime Agency (NCA) said the 29-year-old simply enjoyed inflicting pain, describing him as one of the most prolific and depraved offenders they had ever encountered.
They estimate he had more than 50 victims over a period of eight years from 2009 to 2017.
A "sadistic and manipulative" man, Falder admitted 137 charges out of the 188 against him, ranging from encouraging the rape of a four-year-old to possessing a paedophile manual.
One of the officers involved in hunting Falder down, Will Kerr, of the NCA, said in all his 28 years of policing he had never encountered a more "dangerous individual".
Supervising senior investigations officer Scott Crabb, of Homeland Security in the US, described him as a "monster" and "pure evil". He said: "Falder is absolutely the worst child exploitation and blackmail offender I have ever seen."
'World's worst website'
Falder was caught thanks to the culmination of work by agents which first began in the United States in 2013, as the FBI worked to expose users of dark web paedophilia sites.
Specialists built their own websites on the servers which hosted the offending sites to track what was being said and done on them.
In doing so, they were able to access the so-called hurtcore communities who are defined by their sharing of images of rape, murder, sadism, torture, paedophilia, blackmail and humiliation.
'Hurt 2 The Core', described by the NCA as "the world's worst website", was one such site.
A user known only as "Inthegarden" posted blackmail pictures of a teenage girl. The user was tracked online and found to have also made posts on online marketplace Gumtree.
There, the suspect approached potential victims by masquerading as a depressed female artist. He went by the names Liz, Jess and Shona to lure victims into talking to him, using at least 30 different email addresses encrypted via services which originated in Russia.
He promised hundreds, sometimes thousands of pounds, which he never paid, for naked or partially-clothed images of people. After building a rapport with them, he would obtain their personal information and immediately move the conversation away from Gumtree's servers.
His victims would then be blackmailed into sending increasingly horrific images, with Falder threatening to send them to friends and relatives if they did not submit to his demands.
Victims as young as 14 years old were told to strip naked, write racist and homophobic messages on signs and take pictures of themselves with them.
Others were forced to lick toilet seats and used tampons as well as eat dog food. Some were forced to pose in their school uniforms. These images were then posted on hurtcore forums where they could be seen by countless members of global child sex abuse networks.
Not only this, but the suspect also offered advice to other paedophiles on how to evade capture, suggesting they avoid using money but instead use "vouchers to get kids to trust you".
Many of the suspect's UK victims reported abuse by Inthegarden to police, but there was not enough evidence to identify who was behind the username.
Then in April 2015, the NCA discovered someone posting under the username "666devil".
666devil used a picture of a young girl as his icon on the forum, claiming she was his "daughter". He said he planned to "torture" her during what he dubbed "hell week" and requested ideas from members about what he could do to her.
Officers scrambled to identify the girl in the profile image, accessing the user's webmail accounts to find out who she was and protect her.
That was when they realised 666devil, evilmind and Inthegarden were the same person, and that whoever they were, they had approached more than 200 victims worldwide, including victims living in the US.
However, at this stage, there was still not enough intelligence to identify the suspect.
A special taskforce involving the NCA, GCHQ, Homeland Security Investigations in the US, the Australian Federal Police and Europol - as well as law enforcement in Israel and Slovenia - was set up specifically to "enhance evidence gathering against the suspect".
It proved to be successful as, by the end of March 2017, intelligence linked a person of interest to an address in Birmingham.
Falder was identified as the suspect in April and placed under covert surveillance for three months. He was filmed on the train, using his laptop.
NCA officer Matthew Long said Falder was a "highly manipulative" and "sadistic" man who boasted he would never be caught.
However, he could no longer evade justice and on 21 June last year plain clothes officers were deployed to capture him, arresting him at his workplace.
He was handcuffed in his office at the University of Birmingham, with footage from the arrest revealing how he described the charges against him as the "rap sheet from hell".
Two of Falder's devices were immediately seized, revealing what the NCA called "significant evidence". They showed that Falder's offending went back to 2009, when he was a 21-year-old student.
Police found these early voyeurism offences in fact took place at a total of eight locations, involving 13 victims.
Falder was questioned by police over three days, during which he largely refused to comment but did admit to controlling the evilmind account.
His home in Harborne Park Road, Edgbaston, was raided, revealing a chaotic student-like living space, an untidy bedroom with laundry, old pizza boxes and coins scattered across the carpet.
A desktop computer and laptop were also found, surrounded by drawers of tools and masses of wires stuffed into bulging plastic containers. Officers found information on the devices often had double layers of encryption.
Throughout June and August of last year, the Crown Prosecution Service (CPS) worked with authorities in the US, eventually deciding to prosecute Falder in the UK.
He admitted and was charged with 137 offences in October last year, making him one of the country's most prolific paedophiles, according to BBC Home Affairs Correspondent Danny Shaw. A further 51 charges remain on file.
August 2013 - FBI begins its investigation into dark web paedophilia sites, identifying user known as Inthegarden and passing files to the NCA
April 2015 - The NCA investigate 666devil with "daughter" icon posting on a dark web forum. Officers discover links between 666devil, evilmind and Inthegarden while seeking to "safeguard" the girl
August 2015 - Suspect's webmail accounts are accessed, identifying the girl in his profile and further US victims. Taskforce set up between NCA, GCHQ, Homeland Security, Europol and Australian Federal Police
March 2017 - "Person of interest" identified at an address in Birmingham
April 2017 - Falder identified as the suspect
June 2017 - Falder arrested while at work at the University of Birmingham. Devices seized and Edgbaston home raided. Three days of questioning reveals Falder is behind 666devil
June to October 2017 - Falder admits to and is charged with 137 offences. A further 51 remain on file
Documents released by the CPS and the NCA show that during Falder's near-decade of offending, his multiple victims included boys, girls, men and women.
Ruona Iguyovwe, of the CPS, said: "He sought out his innocent victims on Gumtree and even targeted victims on pro-anorexia websites."
To get what he wanted, Falder posed as a teenage girl on these websites to obtain images of six girls.
Ms Iguyovwe added: "He enjoyed humiliating his victims."
Some victims said since coming into contact with him they had attempted suicide multiple times. Others said they would never get over what happened, that they would always feel "dirty, like used goods".
Analysis: Sima Kotecha, BBC Midlands correspondent
Matthew Falder's case raises further questions about how police can stay one step ahead of those with such an advanced technical knowledge that they're able to exploit the most vulnerable and expose them.
He was a manipulative person whose prime motivation was power and control. He wanted his victims to feel embarrassed and humiliated.
His in-depth knowledge of the internet meant he could post obscene photos in a space only visible to a restricted audience.
The National Crime Agency worked with its international partners to identify the man behind the pseudonyms but he managed to carry out his crimes for several years without detection.
A mother, who gave Falder photographs of her daughter, said: "I was physically ill when I found out that my child's image had been coerced from me and was so shook up that I was in no fit state to go into work.
"I feel as if I failed my daughter massively by being too trusting, as it is my job as her mum to protect her and I put her in danger.
"That will never go away and it is something I have to live with and struggle with the guilt for the rest of my life."
Clinical and forensic psychologist Kirsty Lowe said Falder took pleasure from torturing his victims.
"He refers to enjoyment," she said. "He said he enjoys seeing the reluctant look on her face, seeing how far he could push the person."
Other victims are of course unable to speak for themselves, as Falder shared images of baby torture, Birmingham Crown Court was told.
A spokesman for website Gumtree said it maintained strong relationships with law enforcement and had given its "full support and co-operation to the NCA in their investigation of this case".
Senior investigations officer for the NCA, Matt Sutton, said that Falder's "victim targeting" showed "organisation and advanced manipulation".
He added: "His primary motivation was for power, control, suffering and humiliation. Believing he had superior intellectual and computational abilities, he was confident that he could outwit law enforcement.
"There is little doubt that Falder would have continued his offending, causing untold pain and distress to many other vulnerable people."
GCHQ said it was "an horrific case" and that the hearts of its staff "go out to the victims".
"GCHQ is determined to use our expertise to counter this type of terrible online child sexual abuse."
Steven Wilson, head of department for the European Cybercrime Centre at Europol, said he was "proud to have been able to have contributed to bringing this offender to justice".