A former teacher from Ellesmere Port who investigators said stockpiled more than 43,000 indecent images of children, including AI-generated material, and wrote his own “paedophile manuals” has been jailed for three and a half years following a National Crime Agency investigation.

The National Crime Agency said Charles Cornelius, 57, was sentenced at Chester Crown Court after pleading guilty to offences including making, possessing and distributing indecent images of children, as well as possessing the self-written manuals.

Investigators began looking into Cornelius after receiving information that an online account linked to him had uploaded ten indecent images of children to the internet when he visited the UK in June 2022, the agency said.

The National Crime Agency said Cornelius had been permanently living and teaching in Thailand at the time, and that he was arrested at Manchester Airport on 9 August 2023 when he returned to the UK.

The agency said he gave “no comment” in interview and was released on bail with conditions. Magistrates refused an application for him to return to Thailand while the investigation continued, according to the National Crime Agency.

Officers who examined Cornelius’s devices found a large collection of known child sexual abuse material as well as AI-generated images, the agency said. They also found prompts used to create AI images.

The National Crime Agency said two self-generated “paedophile manuals” were discovered “despite attempts to encrypt devices and conceal the material”.

The case has drawn attention to how generative AI can be used by offenders to create abusive imagery, with investigators highlighting the presence of both AI-generated material and written documents they said demonstrated intent to harm children. The National Crime Agency has warned in general terms that online offending can include the creation, possession and distribution of child abuse material, and that it can cause lifelong harm to victims.

In Cornelius’s case, the National Crime Agency said he had previously taught young children in multiple countries. It said it was believed he took a course in teaching English to non-native speakers before working with the British Council in Thailand from 2012 onwards.

The National Crime Agency did not say in its account that there were identified victims linked to Cornelius’s collection, but said he had placed himself in positions of trust around children while stockpiling and creating abusive content.

In a statement released after sentencing, Danielle Pownall, an NCA operations manager, said: “Cornelius sought out and created images showing horrific abuse of children, including using AI to create further depraved imagery.”

Pownall added: “His creation of paedophile manuals reflects a disturbing desire to prey on the most vulnerable in society. He did all this whilst putting himself in a position of trust around children.”

She said: “The NCA is committed to prosecuting criminals who engage in child sexual abuse activity and pursue justice for victims.”

According to the National Crime Agency’s account, Cornelius pleaded guilty to all charges at Manchester Magistrates Court in September before being sentenced at Chester Crown Court on 11 December.

The agency said its investigation began with information about uploads from a linked account and then expanded into the analysis of devices, which uncovered the scale of the material in Cornelius’s possession and the presence of AI-generation prompts.

The National Crime Agency said the discovery of the manuals came alongside the digital material, and that the documents were found even though investigators said there had been efforts to encrypt devices and hide content.

The case also underlines the role of international travel in some online-abuse investigations, with the National Crime Agency saying Cornelius was living abroad and returned to the UK when he was arrested, and that he later sought permission to return to Thailand during the investigation but was refused.

The National Crime Agency did not provide details in its published account about where the indecent images originated or the ages of children depicted, beyond describing the material as indecent images of children and child sexual abuse material, including AI-generated content.

In recent years, UK law enforcement has repeatedly emphasised that the production and distribution of indecent images, as well as the use of technology to facilitate abuse, remains a significant threat, with agencies urging the public to report concerns and highlighting specialist units focused on child protection.

Cornelius, the National Crime Agency said, was investigated after the alleged upload of ten images to the internet during a UK visit, with officers later uncovering what they said was a far larger cache across his devices.

The agency said he was sentenced to three and a half years in prison. It did not provide further sentencing remarks from the judge in its published statement.