For millions of ordinary fans, hit US crime drama Dexter has been the perfect binge-watch at the end of a long day.

But for a twisted minority, it has ceased to be entertainment and mutated into something far darker: a twisted inspiration for real-world violence.

Within just three months, two British killers who styled themselves on TV serial killer Dexter Morgan have been convicted of gruesome murders – while a 16-year-old obsessed with the show was convicted of attempting to murder a girl he did not even know in school.

The boy, who cannot be named for legal reasons, was just 15 when he approached his female victim in a corridor at Thorpe St Andrew School while wearing a balaclava, plunging a knife into her back before fleeing the scene.

His two-week-long trial heard he had a 'dangerous interest in killers and killing'; he created video compilations of both real and fictional serial killers, including Dexter, and craved what he saw as the 'admiration' they got for their crimes.

Just two weeks earlier, forensics student Benjamin Day, 20, admitted to murdering Maria Saceanu, 24, after luring her to a plastic-lined 'kill room' inside a West Midlands Airbnb, inspired by his obsession with the TV show.

His confession came just weeks after another Dexter-inspired serial killer, James Desborough, 40, was convicted of murdering and dismembering two men in his remote woodland cabin in Cornwall.

Astonishingly, two other Brits, Steven Miles and Mark Howe, Canadian film-maker Mark Twitchell, American teenager Andrew Conley and Norwegian Havard Nyflot have all been convicted of killings inspired by Dexter since 2009.

Dexter, which first aired 20 years ago, follows the life of Dexter Morgan, who by day works as a blood-splatter analyst for the police, and by night transforms into a vigilante serial killer who is expertly equipped to cover his tracks.

Criminologists have warned that the show – which has produced three spin-offs – could be providing a 'how-to script' for copycat killers and would-be murderers.

Alex Iszatt, a behavioural criminologist, told the Daily Mail: 'Dexter gives them a ritual. They can fully become him: follow the same code and principles, wear the same clothes, and use the same methods of killing and disposing of bodies. 

'Dexter provides a usable identity. They are ready to perform to an imagined audience. They are Dexter.'

His actions are strictly governed by a twisted quasi-ethical set of rules taught by his adoptive father, known as 'The Code'. He can only kill proven murderers that have evaded justice – and he can never get caught.

In the show, Morgan feels an uncontrollable, innate urge to kill – which he describes as his 'Dark Passenger' – and follows a meticulous routine, using his police network to research suspects beforehand.

His modus operandi is to prepare a 'kill room', wrapped completely in plastic sheets, to catch all evidence and blood. He tapes photos of the victim's crimes to the walls, forcing them to look at what they have done.

Finally, he murders them and dismembers their bodies before dumping them deep in the ocean.

'What makes Dexter particularly useful to a violent personality is that he provides a justification for killing,' Ms Iszatt adds.

'You're not a monster with uncontrollable urges; you're a vigilante, with standards, and the people you kill deserve it. It doesn't matter if they happen to be your mother, brother or girlfriend.

'There's something inherently appealing about Dexter's dual identity; he is a dark version of the superhero fantasy, respectable and ordinary by day, secretly powerful and dangerous by night. He is Batman.

'For someone fascinated by control, violence and getting away with things, the fantasy is not simply being a killer, it's doing what everyone else can't, while remaining invisible.'

This week, the series was thrust back into the spotlight after a 16-year-old boy was convicted of attempted murder after stabbing a girl he did not know in the back with a kitchen knife in a horrifying unprovoked attack on March 11.

He was arrested by armed police shortly after fleeing Thorpe St Andrew School, near Norwich. His victim, who was also 15 at the time, miraculously escaped with only minor injuries to her back and was discharged from hospital the next day.

He was convicted of attempted murder after prosecutors successfully argued that he had intended to kill the girl – backed up by a cache of evidence police found at the boy's home that showcased an obsession with serial killers including Dexter.

Prosecutors said he was obsessed with serial killers and had written in a note to himself that he had 'seen serial killers being admired... I want admiration, gratification. I've wanted this for years. I don't care who I hurt. Not anymore.'

He made a similar video of actor Jamie Dornan as Paul Spector, a serial killer in the BBC2 series The Fall who, like Dexter, leads a double life: by day he is a bereavement counsellor but by night operates as a sadistic, sexually motivated murderer.

The teen also produced a 'fancam edit' of Dornan in character – a slick compilation  of clips usually made by fans of actors and pop stars to share with fellow admirers – which he captioned 'me btw (by the way).'

It featured Dornan removing a mask he fashioned out of a neck gaiter and a beanie hat – giving him an appearance not dissimilar to the balaclava the teenager wore on the day he attacked his victim.

He also created a bizarre AI-generated video of US multiple killers Edmund Kemper and Ted Bundy dancing on top of a picture of the Earth alongside a third unidentified individual.

Other notes found by police expressed 'hatred for women' following the 'failure of a relationship', and hinted at a possible motive with thoughts on 'misanthropy, misogyny, suicide, bullying'. 

He is also said to have made a 'victims list', and wrote an essay on arming himself with a knife and stabbing a man to death in the street.

Some of the material was found in a shoebox that appeared to have been stabbed. 

In his opening speech, prosecutor Christopher Paxton KC said the boy had an 'obsessive and dangerous interest in killers and killing' and a 'hatred for women'.

He added: '[He] went to school not to learn but to kill, taking with him a kitchen knife.'

The teenager was convicted unanimously of attempted murder, and faces sentencing on December 18.

It is the third time in recent weeks that Dexter has been linked to horrific crimes of violence in Britain.

Earlier this month, University of Worcester student Ben Day violently stabbed Maria Saceanu 78 times to death before attempting to dismember her in an act directly inspired by the TV series. 

He changed into a khaki top similar to that worn by the character and prepared a copycat 'kill room' in what was planned to be a 'tribute' to the show he planned to share online.

The murderer, who changed his university course from journalism to study forensics and applied biology, also had a 'shopping list' of items required for the killing, including plastic sheeting, a staple gun, cleaning chemicals and microscopic slides.

Police said Day 'had an obsessive personality and had become obsessed with the character Dexter'.

Listing 'similarities' between the death and the TV series, prosecutor Rachel Brand KC told jurors: 'Dexter Morgan works as a forensic scientist in a police department – and the broad premise of the programme is that he is a serial killer who knows how to cover his tracks.

'As you know the defendant changed his university course… to study applied biology and forensics.

'He had changed into 'Dexter' clothing before Maria Saceanu arrived at the house.

'In the TV series Dexter prepares a 'kill room' when carrying out his attacks, lined with plastic sheeting which he fixes using a staple gun or duct/gaffer tape.

'And this is exactly how the defendant had prepared the room.

'Dexter wears an apron, a plastic visor and gloves when killing his victims – all such items were found in the bedroom.'

Other similarities with the TV series included a canvas roll containing knives found in the bedroom, the dismemberment attempts and microscope slides thought to be a 'trophy' from the killing, Ms Brand said.

Ms Iszatt, a former crime scene investigator, said the 'kill room' is particularly significant because it turns murder into a ritual of control.

'On the show it's clean, sterile and methodical; the plastic sheeting and protective clothing are presented as solutions to practical problems,' she added.

'For someone interested in forensics, it also feeds a fantasy of competence: not simply being capable of killing, but being clever enough to outsmart the police afterwards.'

The University of Worcester, where Day studied, boasts of 'state-of-the-art research labs and dedicated crime scene simulation house provides immersive settings for working through real-world scenarios'.

They tell prospective students: 'You'll get to use industry-standard geophysical equipment for detecting concealed burials, crime scene investigation kits and specialist fingerprint-enhancing tools.'

A spokesman for the university said it was 'deeply shocked and saddened by this terrible crime'. 

Ms Iszatt said the clothing Day was wearing was 'not merely practical, but a uniform'.

'Putting them on marks the transition from the ordinary person into 'the other' - the forensic-genius killer - creating a psychological distance from the act and making the fantasy feel more real'.

Day's guilty plea came just 70 days after another Dexter fanatic James Desborough was convicted of murdering homeless men Claudio Aquilino, 57, and Daniel Coleman, 43, followed by his prison cellmate, Steven Kempster, 65, while awaiting trial.

The former builder befriended the two vulnerable men at a homeless shelter, before killing and dismembering them at his woodland cabin near Sticker, Cornwall. He used their bank cards and made journeys to create an illusion they were still alive.

Desborough was present at various points during police searches for the bodies and mentioned casually to a forensic biologist on the scene that he 'particularly enjoyed the dismemberment scenes' in Dexter.

Prosecutor Ahmed Hossain KC told jurors: 'That is a series which involves scenes of dismemberment and disposal of bodies.

'There are many, many people who are fans of the television programme Dexter but... when you consider that comment by Mr Desborough together with the fact that two dismembered bodies were found on his land, that the comment takes on a particular significance.'

This is at least one of seven Dexter-inspired killings in the last 17 years.

In 2014, British teenager Steven Miles, who was obsessed with the TV serial killer, was jailed for at least 25 years for murdering and dismembering his 17-year-old girlfriend Elizabeth Thomas.

Miles's trial heard that he had a fixation with horror movies and wanted to copy the actions of Dexter Morgan.

The same year, Mark Howe, then 21, was jailed for at least 21-and-a-half years for murdering his mother, Katrina Wardle, at their home in Leicester.

He stabbed her more than 53 times in the face, mouth, neck, chest and arms after a row over his cannabis smoking. The judge described the attack as 'akin to torture'.

It later emerged that Howe had been secretly sending his friends text messages about hating his mother and began stabbing the punch bag in his bedroom while also becoming obsessed with Dexter.

'He was a fanatic for the programme,' the victim's husband, Kris Wardle, later revealed. 'I mean, Dexter is a serial killer.'

Howe had used a photo of Dexter with a blood-splattered face as his own Facebook profile picture and had searched 'Dexter's kill knife' before carrying out the murder.

In 2008, two years after the series first aired, Canadian film-maker Mark Twitchell murdered Johnny Altinger, 38, in Edmonton, Alberta, Canada, and dismembered him after luring him to his death on a dating website, Plenty of Fish.

Twitchell was dubbed the 'Dexter Killer' due to his obsession with the show and its lead character.

At the time, Michael C Hall, the actor who played Dexter, denied the show glamourised killers.

'I would hope that people's appreciation was more than some sort of fetishization with the kill scenes,' he said.

Referencing Twitchell, he said: 'I wouldn't stop making Dexter because someone was fascinated by it only in that way. I try to tell myself that their fixated nature would have done it one way or the other, but it seems that Dexter had something to do with it. It's horrifying.'

In May 2013, it was reported that Twitchell had bought a TV for his prison cell, where he would catch up on every Dexter episode he had missed.

In 2010, American teenager Andrew Conley was handed a life sentence for strangling his ten-year-old brother to death in Indianapolis. He strangled him for 20 minutes in the kitchen before wrapping his brother's head in two plastic bags and dumping the body.

Conley told police he had fantasised about killing and a few weeks before, he told his girlfriend that he wanted to be just like Dexter.

Also in 2010, 26-year-old Faiza Ashraf was kidnapped, murdered and buried in a shallow grave in Asker.

During the investigation, one of the killers – Havard Nyflot – claimed he had been inspired by Dexter and had decided the victim was a 'bad person' who deserved punishment.

Nyflot and his co-defendant were jailed for 18 and 19 years respectively.

Ms Iszatt said Dexter 'gives vulnerable individuals a language for explaining their own violence'.

'The narrative of the 'Dark Passenger' presents the violent part of Dexter as something that exists within him and demands expression.

'For someone already experiencing violent impulses, that can become a convenient way of understanding and separating themselves: the violent part of me is not really me; it is something that happens to me.

'The show doesn't explain why these people wanted to kill - they have pre-existing psychology, fantasies and circumstances - but it provides a language, an identity and a practical template through which those existing impulses are expressed.'