Detectives know who delivered the fatal blow – the then 16-year-old Jay Murray, who has since been convicted of culpable homicide.

What they don't know – and will never understand – is why the rivalry between the youths of Niddrie and the Southhouse area had to spill over into tragedy.

After his death, members of the Young Niddrie Terror created a Bebo tribute site in his memory.

The site featured a picture of Liam – who had been due to appear in court just a week after his death, in December 2006, on charges connected to an earlier stabbing in Little France – holding an axe. Alongside his name are the gang's initials, YNT.

The site of Liam's death had been the scene of repeated clashes between rival gangs in the run-up to his death.

Although the area has quietened considerably since the tragedy, the Brae is still a focal point for underage drinking and antisocial behaviour today.

Sadly the scenes seen there are being repeated across the city, with gangs of youths regularly staging pitched battles – often pre-arranged by mobile phone or over the internet – and using a frightening array of weapons.

Police have investigated street fights involving rival youths armed with baseball bats, knives, metal poles, bricks and wooden stakes over the last 18 months.

The clashes have sometimes involved up to 100 youths.

Some of the most popular sites for these clashes have included the car park behind the Omni Centre, the Corstorphine Retail Park on Glasgow Road and the Meadows. There have also been repeated brawls in parts of Pilton and Muirhouse, as well as around the bridge dividing the Ladywell and Knightsridge estates in Livingston.

The gangs commonly pre-arrange their fights via their Bebo websites, with the final arrangements made by mobile phone to avoid alerting the police, who monitor the sites.

Among the gangs most feared by their rivals are the Muirhouse Casual Fighters, who have a reputation for turning up in large numbers, armed with golf clubs and knives.

Youths claiming links with the CCS – the Hibs football casuals the Capital City Service – have carried out a number of violent attacks in and around Leith.

The Young Leith Team and Young Lochend Shamrock gangs both claim links with the CCS, and are renowned as regular fighters as well as heavy drinkers.

Some of the gangs, including the Young Mental Drylaw, Young Niddrie Terrors, Bar-Ox and Clerrie Jungle, have been in existence in some form for 30 years or more.

The rivalries also stretch beyond the city, with recent clashes arranged between Edinburgh and Glasgow gangs, and the Edinburgh Young Team – who the police hope to ban from Princes Street – are planning to fight the notorious Young Raploch Slade in Stirling in the coming weeks.

EYT member Sean Weir, 18, from Lochend, told the Evening News: "We're going to Stirling to fight boys from the Raploch. We're taking 80 to 100 people through on the train. We'll split up between Waverley and Haymarket, so the police don't spot us."

The youth discos at city centre nightclubs have also proved a magnet for gang trouble. While strict door policies tend to ensure the events themselves are relatively trouble-free, fights often break out in the surrounding streets afterwards.

Police are staging a crackdown on disorder surrounding youth discos over the coming weeks.

The move comes after clashes between youths travelling from Lothian towns, including Bathgate, Bonnyrigg and Dunbar, and Edinburgh gangs.

Police will be organising bus checks on all the main arterial routes into the city centre to detect any antisocial behaviour, drinking, drugs and offensive weapons among young people travelling to the discos.

There are dozens of Bebo websites set up by youths boasting of the exploits of Edinburgh gangs, although none exist for some of the more notorious gangs.

The sites are used to taunt other gangs, set up fights and voice crude racist – including anti- Polish – and homophobic views.

Police monitor the sites but warn against taking all of them too seriously.

Superintendent Lesley Clark said: "It's sometimes unclear whether these are gangs or virtual gangs that only exist on social networking sites. And it may just be kids who hang around together in certain places.

"We try to engage with youngsters through the Neighbourhood Action Teams, who deal with youth and antisocial disorder. It's not just about chasing them around. It's about changing the culture of behaviour. Officers are often able to build up good relationships with some of the kids.

"The availability of alcohol can be the major factor behind much of the disorder. That's why we work to confiscate alcohol from groups and carry out test-purchasing to stop shopkeepers from selling it to those who are underage."

APPRENTICESHIPS FOR CAREER CRIMINALS
THE youth gangs of Edinburgh have long been a breeding ground for the hardened criminals running the city's drug trade.

Today's teenage gang members know many of the violent criminals in the north of the city and the Inch who are locked in a violent feud over drugs.

Some of the gangs, such as the Young Leith Team and Edinburgh Young Team, are known to be involved in small-time drug dealing.

The most infamous graduate of the city's gangs is perhaps George "Dode" Buchanan, who became one of the city's biggest heroin dealers after learning his trade with the Niddrie Young Terror.

The 50-year-old former body builder was locked up for eight years in 1974 as a teenager for attempted murder, and later for 12 years for heroin dealing.

Would-be hitmen Marc Webley and James Tant were both members of the Young Mental Royston gang. They were jailed in 2005 for the shooting of convicted drug dealer Peter Simpson.

Webley, then 20, already had 60 convictions to his name, dating back to his early teenage gang days, and harboured ambitions to become the major drug dealer in north Edinburgh.