A 15-year-old criminal had already been linked to two violent robberies when he nearly killed another teenager in Verulamium Park.

Herts police were investigating the young man, who cannot be named for legal reasons, in June 2018 when he joined a crowd of teenagers celebrating the end of their GCSE exams on the green.

The good-natured gathering turned nasty when an argument erupted between a group of thugs, including the then-14-year-old offender, and a 16-year-old from London Colney.

When the older boy refused to move to a more secluded area of the park, he was set upon, kicked in the face, and beaten unconscious.

When that victim’s cousin - another 16-year-old boy from London Colney - stepped in, the 15-year-old criminal stabbed him with a 10 inch knife.

The attack inflicted such grievous injuries that the victim had to be airlifted to hospital and have emergency surgery on his gallbladder and stomach.

Although the victim has now recovered, he is lucky to be alive. The first assault victim went to hospital the next day with concussion and facial bruising.

Three teenagers were arrested for the attack, and the stabber was charged with Section 18 grievous bodily harm (GBH), possession of a bladed article, and actual bodily harm (ABH).

After a week-long trial last year, the stabber has been sentenced at St Albans Crown Court to nine years’ imprisonment with a three year licence period - meaning he may spend a maximum of 12 years in jail and will be 27 when the punishment is completed.

In that ruling Judge Michael Kay QC also took into account two other indictments of violent robbery which police were investigating when the incident happened.

The first happened in December 2017 - just six months before the violent GCSE celebration.

At about 5.30pm, two 17-year-old boys went into McDonald’s on Griffiths Way and were approached by a group of males, including the to-be offender.

Prosecuting Douglas Page described this initial interaction as “friendly in an intimidating way”.

Despite trying to call a taxi, the two victims were threatened with violence and forced to accompany the group to Mercers Row.

Robbing and assaulting the teenagers, at least partly because one was wearing a Moncler jacket, the offender was caught on CCTV and later identified by the victims.

Less than a month later, in January 2018, the hoodlum attacked another teenager by Cell Barnes Lane.

On this occasion the victim was unlucky enough to walk past a group of youths including the 15-year-old on his way home. The first sign of threatening behaviour came when one silently blocked his path on a bike.

Navigating around, the victim carried on his journey but with the gang following behind.

As the boy tried to quicken his pace, the 15-year-old criminal grabbed him, held a five inch combat knife to his throat, and led him to a nearby alley.

In the confrontation that followed, the victim was robbed and beaten with the blunt handle of the knife. He suffered a one inch gash to his head and injury to his neck.

The victim remembers a flash of camera while the assault took place, but it is unclear who took pictures.

The 15-year-old pleaded guilty to three charges of robbery in relation to those two incidents at St Albans Youth Court on January 2 and January 16, 2019.

Judge Kay said the stabbing followed an argument over “nothing at all”: “These offences are vicious. They are cowardly because what you did is go in a gang to confront others and what you demonstrated is that you have no sense of what is right and what is wrong.”

He noted a lack of real remorse following arrest, and even said that a DIY toothbrush shank had been found with the teenager’s belongings during a search in custody.

Judge Kay added: “I genuinely hope that you will be rehabilitated, partly for you and partly for society at large because I genuinely fear what you will do if you are not rehabilitated.

“It is possible that you will be dealt with in such a way that you will realise that what you do is evil.”

The Probation Service evaluated the 15-year-old as a significant risk to the public and of committing further offences.

Mitigating Sean Minihan noted his age and influences on the young criminal: “These are all very serious matters and [the offender] knows that. If he was an adult he would be facing an incredibly long period in custody.”

He urged the court to hand down the least possible sentence and give the boy “hope”.

A different 16-year-old offender from St Albans, who was also involved in the Verulamium Park violence, has been jailed for up to a year.

St Albans Ch Insp Lynda Coates said: “The consequences can be devastating when someone decides to arm themselves with a knife and the victim of the stabbing was lucky to survive the violent attack.

“I have no doubt that the traumatic events of that day will stay with both of the young victims and their families for the rest of their lives.

“We are continuing to work with our partners, including schools and colleges, to talk to young people about the dangers and consequences of carrying knives and I would like to take this opportunity to once again urge parents to speak to their children about knife crime and be aware of where they are going and what they are doing.”