A “much-loved” man died at the hands of a teenage gang after a dog fight in a park sparked a vicious attack.

John Hackett, 36, a beloved son, brother, nephew and cousin, walked his dog in a park in Warwickshire every day after get off work.

In April last year, he was attacked to death by three teenagers during a daily walk while 12 others looked on and filmed the violence for “entertainment”.

The 16-year-old girl and two boys, aged 15 and 16, admitted manslaughter and were jailed by Judge Chaudhry KC at Warwick Crown Court in Leamington Spa on Thursday.

Detective Chief Inspector Collette O’Keefe, of Warwickshire Police’s Major Investigation Team, told us independent Hackett’s “haunting” footage of her pleading “will stay with me” amid screams and shouts comes as she warns young people about their use of social media.

“It’s terrible,” she said. “Instead of filming, they should have intervened and stopped what was happening – and maybe John will be here to tell the story.”

Instead, Hackett limped home from Snowhill Playground on the evening of April 25, with DCI O’Keefe describing him as a “walking casualty”.

His body was discovered the next morning by his devastated mother at the top of the stairs at the house they shared in Camp Hill Road, Nuneaton. Emergency services pronounced Mr Hackett dead at 8am and the three offenders were arrested later that day.

Officers believe the senseless death was tragic, unintentional and unplanned.

She said: “It never needed to get to that level. This anti-social behavior eventually escalated over a period of weeks… The people involved did it for their own amusement. I don’t think they thought for a minute that John was going to die.”

She explained the killings shockingly stemmed from an incident when Mr Hackett failed to clean up his dog’s mess. Teenagers linked to the incident began hurling insults at him and his family described how he was “bullied and tortured” over the following weeks.

Officers suspected Mr Hackett was an “easy target” as he reliably walked his dog after get off work every day, so the offenders were aware of his daily routine. He also “looked different”, had long hair and was wearing different clothes than the defendant was wearing.

She said Mr Hackett retaliated against the abuse on the day he was attacked, possibly out of frustration. “That gave the group a green light to go in and attack him,” she said. Evidence from the teen’s cellphone suggested the group planned to verbally abuse him but not physically attack him.

After being called by Mr Hackett and a member of the public, police attended the scene and spoke to the three attackers, who all claimed they acted in self-defence. Police later attended Mr Hackett’s home and found him in severe pain with head and chest injuries and took him to hospital. However, two hours later he was discharged and sent home, where he collapsed the next morning.

Mr Hackett had been beaten and a Home Office post-mortem examination found he died from abdominal injuries of the same severity as if he had been in a car accident.

In a victim impact statement read to the court on Thursday, Hackett’s mother Christine Smith said of her son’s death: “I would say it has ruined my life and put me through hell.”

Nine teenagers watched the game, some of whom filmed the violence and later shared the footage on social media. The girl accused was one of those who recorded the attack before joining in the attack. The harrowing video was widely shared and police warned the public not to share it.

CIA Director O’Keefe blamed the incident, at least in part, on the influence of social media, noting the subsequent widespread dissemination of violence on the platform and the “desensitization” social media can trigger in people.

“The level of violence displayed by these offenders was truly shocking and Mr Hackett must have been frightened,” Detective Inspector O’Keefe said. “Our hearts go out to his family who are understandably devastated by his passing.

“This incident should serve as a warning to people – violence has consequences and sometimes those consequences can be tragic. The three young men may not have intended to kill Mr Hackett, but it ended up happening, just like Hackett Like his family, they will live with the consequences of their actions for the rest of their lives.

“No outcome will change what has happened but I hope Mr Hackett’s family can now begin to rebuild their lives after such a horrific ordeal.”

Hackett’s family paid tribute to him after the sentencing, saying in a statement: “We are devastated by John’s passing. We have lost a much-loved son, brother, nephew and cousin because of a tragic incident. In an act of senseless violence, they were taken from us. John suffered weeks of bullying and torture, culminating in his tragic death. We are reminded of John and what he went through every day.

“We can never forgive those involved.”

All three defendants were sentenced to detention and training orders, which are custodial sentences. A 16-year-old girl from the Nuneaton area was sentenced to 18 months in prison, while a 15-year-old boy from Willencote, Staffordshire, was sentenced to two years in prison, while a 16-year-old boy from Willencote, Staffordshire The boy was sentenced to two years in prison. From Nuneaton, sentenced to two years in prison.