It was 9.10pm and Karen Abramian was returning home to his flat in southwest Moscow. Abramian had been visiting his parents in a nearby tower block. His journey back took five minutes - past a series of grey high-rise buildings soaring into Moscow's packed skyline and a children's playground, and up a modest flight of steps. As he punched in the entrance code, two young men, one wearing a baseball cap and one a bandana, approached him from behind. And then they stabbed him. They stabbed him again - methodically slashing his head, neck, back and stomach. Abramian pleaded with his attackers. "Don't do this. Please take my money," he begged them. His assailants - two slight, boyish, almost nerdish figures - ignored him, stabbing him 56 times. At this moment, Abramian's wife Marta peered out of their ninth-floor apartment window and spotted two boys beating a dark shape lying on the ground. The couple's 14-year-old son Georgy, who had been playing nearby, found his father in the entrance, bleeding profusely. Georgy took off his T-shirt (it was April, still winter in Russia, and bitterly cold), wrapped it around his father and ran upstairs. Abramian was conscious when Georgy came back with a blanket and pillow. Georgy wrapped his father in it and they waited in the gloom for an ambulance. Abramian told his son simply: "They were skinheads." Four hours later, in the early hours of 17 April 2007, Abramian was dead. Doctors had been unable to stem the colossal loss of blood.

The names of Abramian's killers are Artur Ryno and Pavel Skachevsky, both 17. Their motive for murdering Abramian, the 46-year-old boss of a Moscow insurance company, was ideological. As they saw it, Abramian's violent death was part of a national liberation movement - an ambitious, quasi-mystical struggle to get rid of Russia's foreigners, in which they played the role of hero-warriors. The boys had picked Abramian because he was an ethnic Armenian. But his murder was an act of random racist violence: Ryno and Skachevsky spotted him on the street and decided impulsively to kill him. They were apprehended by a neighbour who witnessed the attack and ran after them. They insouciantly escaped on the number 26 tram, but the neighbour, a former investigator, flagged down a passing police Lada and gave chase. Police officers halted the tram and arrested both boys. Ryno and Skachevsky had turned their blood-soaked overcoats inside out; their victim, however, had managed to grab one of them by the arm, leaving behind a bloody print. They made no attempt to disguise their crime; on the contrary, they were proud of it. In their rucksack, detectives discovered 10in knives. In custody, investigators asked Ryno and Skachevsky whether they had committed other murders. To their surprise, the teenagers said they had. In a period of nine months, from August 2006 to April 2007, when they stabbed Abramian, they had killed 20 people and attacked at least 12 others, who had survived. Initially, the police were highly sceptical, assuming that the boys were delusional. Gradually, however, investigators began to confirm Ryno and Skachevsky's fantastic claims. Prosecutors established that the diminutive pair had indeed killed 20 people.

Ryno and Skachevsky are among the worst mass murderers in Russia's modern history. Three hours before Abramian's murder the pair stabbed to death Kyril Sadikov, a Tajik. They ate some food, then set off in search of their next victim. The 45-page court indictment against them shows a disturbing pattern, with the skinheads lying in wait next to different suburban metro stations and stabbing their victims 15 to 60 times. The victims had one thing in common: they weren't Slavs. Most were guest workers toiling in Moscow's building industry or as cleaners in the capital's communal courtyards and urban parks. Nobody knows how many low-wage gastarbeiter are currently resident in Moscow, a teeming metropolis of 12 million people - estimates range from 200,000 to 2 million. Typically, Ryno and Skachevsky's targets had fled poverty and the impoverished former Soviet republics of Central Asia - Tajikistan, Uzbekistan and Kyrgyzstan. Others were from China. A few were "of Caucasian appearance", as the charge sheet puts it, from Russia's troubled southern provinces of Chechnya or Dagestan.

Like all warriors involved in a holy war, as they perceived it, the boys sometimes made mistakes: several of their dark-skinned victims were actually ethnic Russians. One murder sticks out. On 9 April 2007, it was the turn of S Azimov, an Uzbek student. The skinheads ambushed Azimov outside his flat in Moscow's northwest suburb of Voikovskaya. Azimov lived on Zoe and Alexander Kosmodimiyansky Street - named after two Soviet partisans. Moscow's British school is a short walk away, down a busy boulevard; middle-class parents in orange Range Rovers whizz past. Voikovskaya is a blandly anonymous suburb, the kind of place where nothing really happens. The skinheads stabbed Azimov 56 times. As he lay on the ground, his life ebbing away, they cut off his left ear.

Alexander Verkhovsky describes Ryno and Skachevsky's killing spree as "very unusual". Verkhovsky is an eloquent, English-speaking Russian with shoulder-length black hair and a 70s-style suede jacket. He is an expert on xenophobic violence and the director of Sova, a Moscow information centre that logs hate crime. We meet in a Moscow café a few days before Ryno and Skachevsky's five-month trial for murder is due to end. Just round the corner, around 300 neo-Nazi activists are holding a rally beneath a statue of the Russian playwright Alexandr Griboyedov. (Griboyedov is a sort of early skinhead martyr. The author of the verse comedy Woe from Wit, he was stabbed to death in 1829 by a Persian mob.) The skinheads wave black, yellow and white flags; a few clamber on the statue and launch Hitler salutes, shouting: "Russia for Russians".

I later discover that most Russian skinheads revere the Führer, believing that his only mistake was to attack Russia. The average age here is about 15 or 16; the style is baseball caps, Burberry scarves and Lonsdale - the uniform of the British far-right. One skinhead even has a Union Flag jacket. There are several girls. The skinheads adhere to two ultra-nationalist groups - the Movement Against Illegal Immigration and the Slavic Union. A stall shows a photo of 15-year-old Anna Beshnova - a pretty, blonde Russian schoolgirl raped and then murdered in October 2008 by an Uzbek city maintenance worker.

Her death has ignited racial tensions across the city's already flammable lower-middle-class suburbs and inspired several revenge attacks.

According to Verkhovsky, the phenomenon of racist violence in Russia isn't new. What makes Ryno and Skachevsky's case remarkable, he says, is the prolific scale of their murder spree. The fact that the police solved their crimes has nothing to do with their investigative skills, he says, but is down to the teenagers confessing: "This isn't an example of good investigation."

Xenophobic prejudice is widespread in Russia, Verkhovsky says. "More than 50% support the idea that ethnic Russians should have privileges over other ethnic groups," he says. "More than 50% believe that ethnic minorities should be limited or even expelled from their region." Under communism there was prejudice towards non-Slavs as well as Jews, despite the poly-ethnic nature of Soviet life. In the 1990s, when many ethnic Russians returned from newly independent republics like Uzbekistan, prejudice continued. But it is over the past eight years that racism has grown to astonishing levels, Verkhovsky says. Russia's second war in Chechnya and the 1999 apartment block bombings, which killed almost 300 people in four Russian cities, created this new xenophobia. The Kremlin blamed the bombings on terrorist Chechens; others suspect they were the work of the FSB, the former KGB. Either way, racism in Russia is now ubiquitous. According to Sova, 96 people were murdered in 2008 in racist or neo-Nazi attacks, with another 419 beaten or wounded. (The number of deaths was 50 in 2004, 47 in 2005, 64 in 2006 and 86 in 2007.) Last month, another 12 people were murdered. Sova's research suggests that xenophobic prejudice has become mainstream, acceptable. And while most Russians don't support radical ideas in practice, there are around 2,000-3,000 young skinheads prepared to attack and kill migrants, he estimates. Russia's law enforcement agencies, tasked with the job of catching these boy killers, share the prejudices of Russia's general population. Typically, police officers ignore race attacks, or classify them with the lesser charge of hooliganism. Verkhovsky says: "Enforcement is very weak. These young skinheads don't feel fear of the police, since the risk of getting caught is small."

The bloody evidence appears to confirm his grim thesis. A few days before our meeting, an unknown group, the Militant Organisation of Russian Nationalists, sends out a chilling email. The group says it has murdered a 20-year-old Tajik, stabbing him six times as he walked home from his job at a food warehouse. They cut off his head, dumping it in a bin outside a council office in western Moscow. The victim's body was discovered near the village of Zhabkino, a few kilometres outside the capital. The email includes an attachment. It is a photograph of the young man's head lying on a giant wooden chopping block. The group says the murder is a protest against authority for its failure to deal with immigration or - as the killers put it - to rid Russia of its Caucasian and Central Asian "occupiers". Unless government officials deport "the blacks" their heads would "fly off" next, it warns. The beheading is reminiscent of another gruesome neo-Nazi attack that surfaced last year on the internet via far-right websites. The video - entitled "The execution of a Tajik and a Dagestani" - shows two men kneeling in an autumnal Russian forest, bound and gagged under a Nazi flag. Masked men saw the head off one man and shoot the other. Russian investigators initially dismissed the video as a hoax. Later, however, it emerged it was genuine. A man recognised the Dagestani victim as his missing brother; he had vanished in Moscow several months earlier. During the same week in December 2008, unknown assailants in the southern city of Volgograd casually knifed a black American teenager. Stanley Robinson, 18, from Providence, Rhode Island, had been in Russia on a school exchange. The attack left him critically injured and he was flown out of Russia to Finland for emergency surgery. Back in south Moscow, suspected skinheads stabbed an 18-year-old Kazakh student, Yerlan Aitymov, as he waited for a bus near Kaluzhskaya metro station. Yerlan died on the way to hospital.

Artur Ryno and Pavel Skachevsky do not fit the profile of classicserial killers. There isn't much in their upbringing to suggest they will turn into flamboyant teenage murderers. Ryno grew up in the southern Urals city of Yekaterinburg. His parents divorced when he was young; his father is from Russia's Far Eastern province of Chukotka. (Ironically, Ryno's own features are slightly non-Slavic.) At school Ryno showed an aptitude for drawing; classmates describe him as a quiet, introverted pupil who struggled to make friends. His lawyers claim he fell under the sway of racist ideas after a Chechen schoolmate beat him up. In 2006 Ryno moved to Moscow, where he enrolled in Moscow's arts institute and studied icon painting. (Several of Ryno's icons hang in the church in Yekaterinburg, built on the spot where the Bolsheviks shot Russia's last tsar and his family.) In Moscow, Ryno shaved off his hair. He met Skachevsky via an ultra-nationalist website, www.format18.ru (the numbers 18, of course, correspond to Adolf Hitler's alphabetic initials). The forum is popular with teenage skinheads who use it to swap videos of their racist attacks.

Skachevsky grew up in Moscow. The son of a deputy headmistress, he was a gifted student. Like Ryno, Skachevsky hates "blacks" - claiming that several of his friends perished in the 1999 Moscow apartment block bombings. "I live in the house opposite Guryanova Street, and the block which the Chechens blew up," he told friends. At the time of the murders Skachevsky was a student at Moscow's college for physical education. Together, the pair formed a gang of around a dozen like-minded skinheaded killers. They are a geeky-looking bunch - the tallest is a girl, Svetlana Avvakumova, 22, who videoed one of the gang's brutal attacks on a Chinese youth. Several wear glasses. Police got round to arresting Avvakumova in February 2008.

The trial of the Ryno/Skachevsky gang began last July at Moscow's city court. Outside court, I meet Avvakumova's mother, Yelena, who has turned up hoping to catch a glimpse of her imprisoned daughter. Yelena is baffled at her daughter's involvement, denying that Svetlana has anything to do with skinheads. After her arrest, however, detectives showed her the video, which faithfully records how the gang mercilessly kick and knife a Chinese boy as he lies on the ground. The boy is crying. Avvakumova downloaded the film on her home computer alongside snaps taken on the monastery-lake island of Valaam during a holiday in Russia's picturesque north.

"Svetlana was always an innocent," Yelena says. "As a girl she was a bit of a tomboy. She liked football and used to watch Spartak Moscow FC." Intriguingly, Yelena has a strong sense of where her daughter has gone wrong. Skinheads are something of a paradox in Russia, a country that sacrificed 25 million people in the fight against Nazi Germany and the ideas of racial supremacy. "My father was a tank commander during the war. He was severely injured during the battle for Königsberg; it left him disabled. He personally fought fascism. Svetlana understands perfectly what fascism is. We still have her grandfather's medals." According to Yelena, attitudes changed after the collapse of the Soviet Union. "My generation was a Soviet one. We were internationalist. We have Armenian relatives. My brother even married a Japanese woman. The problem is with this new generation. They don't understand the difference between nationalism and patriotism. They confuse the two."

Dmitry Dyomushkin is wearing a Ben Sherman T-shirt; he's ordered a plate of kebab and a bowl of borsch - beetroot soup. He speaks Russian with a slight impediment, and lights a cigarette after every mouthful. Dyomushkin is the leader of the Slavic Union, Russia's most radical ultra-nationalist organisation. Aged 30, he is a veteran of Russia's far-right scene. We meet in a pub in Marino, a sprawling dormitory suburb in southern Moscow, full of tower blocks and at the end of Moscow's light-green Metro line.

Both Ryno and Skachevsky were members of the Slavic Union. (In Russian the organisation is called the Slaviyansky Sayuz, the SS.) "I didn't know them personally," Dyomushkin says. "They were young guys sitting in the corner of the meetings. They were quiet, mouse-like." His organisation has 1,500 members across Russia, though experts suggest the number of far-right activists is around 50,000. The SS fights against illegal immigration and for the rights of Russians in Russia. Dyomushkin says he has been disappointed by the radical actions of many of his members - more than 100 of them have been arrested and several are now serving life sentences for murder. (One of the group's leaders, Nikola Korolev, was jailed for blowing up Cherkizovsky market in Moscow in August 2006, killing 14 people and wounding 49 with a bomb left outside a Vietnamese café.) "These tactics were wrong," Dyomushkin asserts.

Dyomushkin is at his most plausible when he talks about the threat the Slavic Union now poses to Vladimir Putin. Over the past eight years Putin has squeezed out virtually all independent political activity in Russia. There are now only two opposition movements left, Dyomushkin argues - the far-right and the democratic liberals. Dyomushkin is scornful of the liberals - "many of whom are Jews" - but agrees they share anti-Kremlin ideas. But while the democrats are weak, divided and marginalised, the nationalists enjoy much broader support - including that of elements deep inside Russia's powerful bureaucracy and law enforcement agencies. (Both Ryno and Skachevsky had links with a former far-right deputy in Russia's Duma, or parliament. Officially they were working as his parliamentary researchers.) Dyomushkin describes Putin's Russia as a "police state", which has retained the worst aspects of the Soviet Union while getting rid of the good bits. "It may seem a paradox, but our movement is now fighting for freedom. It is the nationalists who are fighting for freedom of speech and assembly. Nothing else has the strength to do this. Everyone else is frightened," he says.

In November 2008, police and federal security agents broke up the Slavic Union's annual "Russian March", arresting 1,000 people, including Dyomushkin. He was released after several hours in custody, however, and eventually fined a paltry 1,000 roubles (£23). Russia's authorities are clearly rattled by the rise of the far-right, whose political appeal is likely to grow as the country slithers into economic crisis. As living standards tumble it is immigrants who will get the blame. There is no prospect of a pro-western Orange Revolution in Russia. But the possibility of a far-right revolt against Putin is real and growing. The skinheads - a pimply, adolescent army of lower-middle-class racists - pose a serious threat to the Kremlin's otherwise

vice-like grip on power.

In December 2008, Ryno and Skachevsky were sentenced to 10 years in jail, the maximum sentence for a juvenile. Five other members of their gang were jailed for between six and 20 years. The jury acquitted Avvakumova and one other male gang member. During the trial the skinheads showed no remorse, giggling frequently and even laughing at the families of their victims. Ryno made a final speech to the jury. In a rambling address, he explained that he committed the murders for the "tsar, country, and monarchy". Later he revealed that after prison he intends to embark on a new career. He wants to be a politician.

Marta Abramian shows off a photo of her husband, taken a month before his murder. As well as their son Georgy, the couple have two strikingly pretty dark-haired daughters, Meline and Karine, now 20 and 21. The photos show Karen dancing with his girls at a party; other snaps show the family relaxing on holiday in Egypt, next to a camel; there are black and white photos of Karen's happy boyhood in Baku, Azerbaijan. The couple met and courted in Baku, but in the late 80s they moved to Moscow when war erupted between Azerbaijan and Armenia. Karen studied at Moscow University and then joined an insurance firm, rising to become its general director. He wrote poems and composed songs. "He was a wonderful father, a wonderful son and wonderful husband," Marta says. "I never thought this could happen to my husband. We considered ourselves real citizens of Russia. We work here. We pay taxes. This is our country."

We meet in the apartment of Karen's parents, Asya, 75, and Georgy, 76. They sit together on the sofa holding their son's framed photo; his murder outrages them still. After an hour punctuated by phone calls from the court - the skinheads' trial is just ending - Marta takes us to the spot where Karen was murdered. Next to the entrance, she has planted a small fir tree; she and the kids still live upstairs on the ninth floor. "It's so we can remember Daddy," she says. "It's very difficult without him. There is just an empty shape. Nothing can fill the emptiness.".