Following a tip-off from overseas agencies, Customs questioned Snell and a phone search located a number of objectionable publications.
He was arrested at the airport by Customs investigators for the importation and possession of objectionable publications.
A forensic search of the phone identified 285 images and 21 video files of child sexual abuse dating back to 2018, including 50 classified as the most extreme category of abuse.
A similar examination of his laptop uncovered various objectionable publications, and links to an online chat forum used by offenders to download, trade, and exchange objectionable child sexual exploitation material.
In court Judge David McNaughton called it a "gross invasion of children's privacy".
He said Snell told a probation officer he had fantasies about sexually abusing the children he taught.
"In my judgment, your offending is extensive. You were found with 50 images and 10 videos."
Crown prosecutor Katie Karpik argued that even though the charge was about possession and not distribution, it was more about the nature of content found.
"There were 10 category A videos and images found on his personal device, a term of imprisonment is appropriate," Karpik said.
Defence lawyer Julie-Anne Kincade QC argued home detention was the most appropriate sentence.
"He will have a conviction and be on the child sex offenders registrar and that speaks for itself."
Kincade also said there was no evidence of the material being accessed since 2018.
"He has had 52 hours of treatment so far and his doctor has expressed the cognitive changes since starting," she said.
But Judge McNaughton said a starting point for penalty at the lower end was "out of the question".
Snell's mother sat in the back of the court after travelling from the UK.
With her head bowed, the woman held back tears as Snell's sentence was given.
Snell is no longer a registered teacher.
Customs child exploitation operations team chief customs officer Simon Peterson said unlike most Customs cases which deal with online exploitation, this was unusual in that it involved an individual attempting to cross the border carrying child sexual exploitation materials.
"Customs remains vigilant at our airports for returning passengers who attempt to import child sexual exploitation material and other illegal goods."
Any publication that promotes or supports the exploitation of children for sexual purposes is deemed an objectionable publication under the Films, Videos, and Publications Classification Act 1993.
Objectionable publications are also prohibited imports and exports under the Customs and Excise Act 2018.
The maximum penalty for the importation or exportation of objectionable publications is 10 years' imprisonment.
In 2020, Customs investigations manager Bruce Berry said there is a global network of law enforcement agencies and partners that work together to stop individuals who commit crimes against children.
"Customs has a dedicated team of specialists who work around the clock to target and catch people who commit cross-border offending relating to child sexual exploitation. While we are based at the New Zealand border, law enforcement has a global reach.
"This should be a further warning to people who commit child sexual exploitation offences – whether you're carrying the illegal material on your devices physically across the border, travelling overseas for child sex tourism, or downloading or uploading objectionable images and videos across the cyber border – Customs will catch you," Berry said.
Budget 2019 has allocated $10.2 million, over four years, to Customs to help boost its efforts to combat child sexual exploitation across New Zealand's cyber and physical borders.
Where to get help
If you have concerns or suspicions about someone who may be trading in or producing child sexual abuse images or videos, contact Customs confidentially on 0800 WE PROTECT (0800 937 768) or Crimestoppers anonymously on 0800 555 111.
If you are, or know of, someone who is at risk or being abused, contact the police immediately.
