It is broad daylight early on a Sunday afternoon and, just as in any other shopping centre up and down the country, The Mall in Luton is packed with families dragging bored children in and out of chain stores.
Suddenly, shouts and piercing screams erupt, the crowd parts and three teenagers start slashing at one another with knives, including a terrifying 18in machete.
Two run off – one of them wounded – as the third boy collapses to the ground with a terrible injury, blood spurting scarlet on to the polished marble floor. By the time security guards arrive at the scene, his life is ebbing away.
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It was nothing more than a 'wrong' look that led to the senseless death of 18-year Azaan John Kaleem – the second violent episode at the heart of tomorrow's documentary
Outnumbered: CCTV shows gang surrounding Azaan and his girlfriend
As one guard tries to stem the flow from a massive gash in the 17-year-old's thigh, he pleads with the boy: 'Hold my hand and keep your eyes open.'
These horrific scenes, caught on CCTV, are a devastating depiction of Knife Crime Britain – a tide of violence rolling across towns and cities across the country.
In Luton, many miles from London's knife crime hotspots such as Islington or Tottenham, cases of stabbings have almost doubled over the last five years.
And no region is immune, with national crime statistics showing 40,000 blade-related incidents across the country in the year to September 2018.
Even this disturbing figure probably understates the total.
Brutal: Azaan is attacked, despite the appearance of a bystander. Shannon runs to escape
The terrifying trend is brought into sharp focus in tomorrow night's special edition of Channel 4's 24 Hours In Police Custody, in which TV cameras follow Bedfordshire detectives as they struggle to tackle a form of crime now so widespread it has become almost routine.
Tom Hamm is the detective sergeant who investigates the bloody Luton shopping centre knife fight.
He tells viewers: 'I'm tired of coming into work thinking, 'I wonder who is going to get stabbed today.' I've never known it in ten years to be as bad as it is now. If you were to equate it to a disease, this would be a national emergency.'
It was nothing more than a 'wrong' look that led to the senseless death of 18-year Azaan John Kaleem – the second violent episode at the heart of tomorrow's documentary.
Azaan had never been in trouble with the police and wasn't even known to the four-man gang that killed him.
He'd been walking through Luton with his girlfriend, Shannon, when he made the mistake of exchanging looks with a boy on a bicycle on the other side of the street.
As Shannon explains it, the other boy put his hand inside his trousers as though to pull out a knife. Azaan reached towards his pocket to show he too was armed.
Felled: Azaan crumples on to the road, fatally wounded in the sustained attack
He had started carrying a knife for his own protection a year earlier after being badly beaten up – a terrible error.
The boy on the bike sped off and the incident appeared to have ended but minutes later CCTV cameras record a grey BMW pulling up alongside Azaan and his girlfriend. Even the police were shocked by the level of brutality that ensued.
Four boys emerge from the car and immediately set upon Azaan. One seems to punch him repeatedly – but is actually stabbing him, probably with a bladed knuckleduster he was later found to be carrying.
Azaan is left lying in the road with multiple stab wounds to his back, chest and face, blood pouring out as the gang flee. He died of his injuries in hospital two days later.
His heartbroken mother, Roseann Taylor, told me about her teenage son's last moments.
'When they declared Azaan brain dead, curtains were pulled around and piece-by-piece they turned off equipment,' she said.
'They allowed me to stand behind him. I stroked his hair and told him I loved him. We waited for his heartbeat to stop.
Left to die: The thugs leave stricken Azaan as the bystander stays to offer help
'When I watched the CCTV and found out they didn't know Azaan, it reminded me of a pack of animals seeking out their prey.
'He was not a person, he was some 'thing' they wanted to attack.'
