Three teenagers have been detained for killing a man they thought was a paedophile by luring him to a Kent beach before one threw rocks and a bottle at him. A 16-year-old girl and a 16-year-old boy were sentenced to seven years in custody, while a 15-year-old boy was handed a five-year term, at the Old Bailey on Thursday, for the manslaughter of Alexander Cashford, 49, in Leysdown-on-Sea on the Isle of Sheppey on August 10 last year.

Prosecutors say Mr Cashford was chased and hit with rocks and a bottle, and was found lying face down in mud. He met the 16-year-old girl at around 7pm on August 10 at the seafront in Leysdown-on-Sea, and just over an hour later he was dead, a trial had heard. Sentencing the trio on Thursday, Mrs Justice Cheema-Grubb said she accepted it started out as a “bit of mischief” of teenagers on holiday, but turned into “dangerous misconduct which risked and ultimately took a man’s life”.

The sentences were passed to a packed public gallery.

Judge Cheema-Grubb told the defendants: "You decided to attack a man that none of you knew and two of you had never met. All he did was give a business card. He did not touch you. You could have thrown it away. If you were concerned [about Cashford], you could have turned to all the adults in your life."

Jurors had unanimously acquitted the teenagers – who cannot be named for legal reasons – of murder following a trial at Woolwich Crown Court in February. But they found the girl and 15-year-old boy guilty of manslaughter, while the 16-year-old boy admitted manslaughter days into the trial.

A post-mortem examination showed Mr Cashford had injuries to his face and head, bruises on his limbs and body, and a number of fractured ribs that had punctured his lung.

A statement from Mr Cashford’s parents read out at the sentencing hearing described him as a “kind, friendly and compassionate person” who cared about local animals and wildlife, and loved all sports.

They said they were “emotionally crushed” and the impact on the family was “practically impossible to put into words”.

They added he was the rock in their life and “the slander against Alex’s name is particularly difficult, we know this could not be further from the truth”.

During the trial, jurors were told Mr Cashford had given the girl his number on August 8, after meeting her by chance at an amusement arcade, and he also handed her a business card with a name on that was not his.

Using the alias Sienna, the three teenagers exchanged messages with Mr Cashford and arranged to meet him by the sea wall.

The 16-year-old boy had saved Mr Cashford’s number in his own phone as “pedo” and around 75 messages were sent between them, the trial heard.

The trial heard when Mr Cashford and the girl met, the two boys followed them as they walked along the promenade in the Isle of Sheppey village before the attack began.

Mobile phone footage showed the older boy striking Mr Cashford on the head with a bottle, before he and his male co-defendant ran after the fleeing Mr Cashford.

Meanwhile, the girl shouted “f****** paedophile, I’m f****** 16, get him” as she filmed the boys chasing Mr Cashford.

Mr Cashford fell and the 16-year-old boy threw a rock at him, which one eyewitness described as “the size of a cereal bowl”, the court had heard.

Afterwards, the older boy shared footage of the attack with three people, with the caption: “f***** pedo (sic) up lol”.

Giving evidence in the trial, he claimed he attacked Mr Cashford because he felt police “wouldn’t have done anything” if they had reported him for trying to meet up with the girl.

On Thursday, representing the boy, Danny Moore KC said he feels genuine remorse for what he did, and asked for the shortest possible sentence for the boy who “couldn’t have had a harder beginning in life”.

During the trial, it was heard the girl and the younger male defendant said there was never a plan to hit Mr Cashford.

Danny Robinson KC, defending the girl, told the trial texting Mr Cashford started as a “big laugh”, and may have turned “into a desire to expose him as someone who should be named and shamed”.

However, the attack was not the product of an “organised plan to kill or cause anyone really serious harm, it was a childish escapade that got out of hand very quickly with tragic consequences”, he said.

At the sentencing hearing on Thursday, Mr Robinson said the girl has thought about what she did wrong and in an expert’s view she is remorseful for her actions.

Meanwhile, for the 15-year-old defendant, barrister Benjamin Newton KC asked for an intense supervision order instead of youth detention for the boy, whom he said “played a minor role” in the incident.

Mr Newton said the youngest boy, who was 14 at the time, did not arm himself when he had the opportunity to do so and his risk of reoffending is low.

During the sentencing, the court heard the three teenagers will serve half of their sentences in custody, with the rest on licence.