A British court sentenced a 30-year-old man to at least 25 years in prison on Monday after convicting him of the sexual abuse of dozens of children while he worked as an English teacher in Malaysia.
The court heard that Richard Huckle, who pleaded guilty to 71 offences, had used his position as a teacher since 2005 to befriend families in Malaysia and gain access to the children he abused, including one who was just six months old.
He filmed some of the abuse and sold material through paedophile forums on "dark web" internet sites, prosecutors said.
"It is hard to put into words the sheer depravity of this case," said Anthony Hill of the Crown Prosecution Service.
"For almost nine years, Richard Huckle subjected at least 23 children, some of them very young, to the most horrifying abuse imaginable," Hill said in a statement following Monday's sentencing.
Police arrested Huckle as he arrived at a British airport in December 2014, following a tip-off from detectives in Australia.
They found more than 20,000 indecent images of children on his computer and cameras. More than 1,100 images "showed him raping and abusing children in his care," the National Crime Agency said.
Huckle had posed as a student, charity worker and photographer at different times, and he created a guide for other paedophiles on how to abuse children and evade capture, the agency said.
"He deliberately travelled to a part of the world where he thought he could abuse vulnerable children without being caught," said James Traynor, a child protection officer from the agency.
The agency had tracked and arrested Huckle using legislation allowing British citizens to be prosecuted for crimes committed abroad, Traynor said.
"Borders are no barrier," he said. "We are determined that those who go abroad to abuse children will be held to account."