“What do you want?” – “To see them die.”

Britain is a key link in the biggest ever international investigation into the production and supply of paedophile 'snuff' movies - in which children are murdered on film - an Observer investigation can reveal.

The key suspect in the inquiry, a Russian who was arrested last week in Moscow for distribution of thousands of sadistic child porn videos and pictures, was traced following the seizure of his products from British paedophiles.

Dmitri Vladimirovich Kuznetsov, a 30-year-old former car mechanic in Moscow, was identified after British Customs and police traced the origin of violent child porn videos found in the UK back to Russia.

Last week Italian police seized 3,000 of Kuznetsov's videos on their way to clients in Italy, sparking an international hunt for paedophiles who have bought his products. The Italian investigators say the material includes footage of children dying during abuse. Prosecutors in Naples are considering charging those who have bought the videos with complicity in murder. They say some may have specifically requested films of killings.

British authorities yesterday confirmed that scores of Kuznetsov's videos, produced in his small flat in Moscow's rundown Vykhino district, have been found in the UK. They are concerned that 'snuff' movies in which children are killed may have also been imported.

Around a dozen British men have already been arrested and charged with offences alleged to be connected to the Russian tapes. A second Russian child porn ring, which allegedly had a British distributor, was broken up earlier this year. The investigation into the importing of violent Russian child porn which led to the identification and subsequent imprisonment of Kuznetsov started about 15 months ago after Customs seized material coming into the country. Since then there have been dozens of other finds.

'We have seen some very, very nasty stuff involving sadistic abuse of very young children, but actual deaths on film takes it a whole step further. That is very worrying,' said one senior customs officer this weekend.

British paedophiles were paying between £50 and £100 for Kuznetsov's tapes, the officer said. Further fees were paid for access to a website that features pictures of extremely violent abuse.

Though two men arrested with Kuznetsov have also been imprisoned by Moscow authorities, only one of the three remains behind bars. Dmitri Ivanov was sentenced to 11 years for actually participating in the abuse that was being filmed. The others were released under an amnesty aimed at clearing Russia's overcrowded prisons.

When officers from the Moscow Criminal Investigation Department raided Kuznetsov's flat they found two boys in a makeshift studio. They seized a huge quantity of films and other pornographic material as well as lists of clients in Italy, Germany, America and Britain.

Last week Italian detectives moved in, following months of inquiries, and arrested eight people. The police searched more than 600 homes and say they now have evidence against about 500 people. Among the suspects were businessmen, public employees and a university student. Several of them were married, with children of their own. Hundreds of people are also under investigation in Germany.

The Russian videos, which had been ordered over the internet, were intercepted when they came into Italy by post, repackaged and then delivered by undercover police officers. They cost between £300 and £4,000, depending on what type of film was ordered.

Covert film of young children naked or undressing was known as a 'SNIPE' video. The most appalling category was code-named 'Necros Pedo' in which children were raped and tortured until they died.

Police in Russia and the UK believe that Kuznetsov and his associates have been in business for more than two years in which time they are believed to have recruited around 100 boys - aged between nine and 15 - to be filmed.

'Most of the children were rounded up from railway stations. A lot of them came from the suburbs, or surrounding regions and were from deprived, problem families,' said Kiril Mazurin, a police spokesman.

'Usually when children like this arrive in the capital, they've got no idea where to go and hang around in the station. It's very easy to entice this kind of teenager - with a promise of a warm bed or a trip to the cinema.'

Many were lured away from orphanages. 'Children are not locked in,' said Mazurin. 'Anyone can come along and promise them a meal at McDonalds. It doesn't take any more than that."

Some children were paid a commission to find other boys willing to be filmed, according to reports in the Russian press, for a fee of between 100 and 300 roubles (£2.50 - £7).

Kuznetsov had given up his job in 1998 to devote himself to the lucrative pornography industry. A self-taught computer expert, he was in the process of upgrading his equipment to allow him to e-mail videos directly to clients when police raided him.

Many customers repeatedly ordered videos from him. The Naples newspaper Il Mattino published a transcript of an alleged email exchange between a prospective client and the Russian vendors.

'Promise me you're not ripping me off,' says the Italian.

'Relax, I can assure you this one really dies,' the Russian responds.

'The last time I paid and I didn't get what I wanted.'

'What do you want?'

'To see them die.'