Interpol has launched an unprecedented global public appeal to help identify a man shown sexually abusing children in photographs posted on the internet.
The suspect is said to be of European origin, and aged 35 to 40
The man appears in about 200 images depicting the abuse of 12 boys, which police said were taken in Vietnam and Cambodia, possibly in 2002 and 2003.
The pictures had been digitally altered but police computer specialists have produced identifiable images.
Interpol says the man is a danger to children while he remains at large.
Interpol chief Ronald Noble said: "We have tried all other means to identify and to bring him to justice.
"We are now convinced that without the public's help this sexual predator could continue to rape and sexually abuse young children whose ages appear to range from six to early teens."
The first pictures of the man were found three years ago in Germany, Interpol said.
The pictures had been manipulated to disguise the man's face with a swirl pattern, but computer specialists at Germany's federal police agency, the BKA, worked with Interpol's human trafficking team to produce identifiable images.
They show a man with slightly receding dark hair, aged 35 to 40 years old.
Despite extensive efforts through Interpol's network of 186 member states his identity remains unknown.
Interpol maintains a database of 520,000 images of child sex abuse submitted by 36 member states.
Using sophisticated software, investigators have identified and rescued nearly 600 victims from 31 countries.