WARNING: This article contains distressing details relating to extreme child abuse, suicide and strong language.

Cimarron Thomas was 12 years old in 2018 when she used her father’s handgun to kill herself.

From West Virginia, USA, she played the violin, she loved elephants and chatting with her friends on Snapchat and was looking forward to her 13th birthday.

But was being sexually abused and blackmailed online by a student from Northern Ireland, described as the UK’s most prolific catfisher.

Alexander McCartney, 26, from outside Newry, County Armagh, has been given a life sentence with a minimum of 20 years in jail for the manslaughter of Cimarron and the extreme sexual exploitation of other young girls.

In a tragic turn of events, Cimarron’s father, Ben, a US army veteran, took his own life 18 months later. He did not know about his daughters abuse or why she took her own life.

Cimarron’s grandparents, Peggy and Dale Thomas, detailed their pain in a victim impact statement read out in court.

“Our lives will never be the same again,” they said.

“We didn’t get to see her graduate, walk down the aisle or have children.

“We have been robbed and our lives have been changed forever.”

Cimarron Thomas lived with her mum, dad and siblings.

They were an ordinary American family but in 2018 a predator was about to bring destruction to their lives.

Using a fake persona, McCartney contacted her online, complimented her on her appearance and began grooming her before she sent him an intimate photo.

The court heard that during the first abusive interaction he kept her online for an hour and 45 minutes, demanding sexual and degrading images.

He told her if she didn’t send him more photos he’d publish the ones he already had on the internet.

Cimarron went back to school and did not tell anyone about the abuse.

McCartney continued to pursue Cimarron and contacted her four days later using another fake account saying: “I want to play one more time.”

Despite pleading for McCartney to stop, and being visibly upset, he told her to “dry your eyes” and involve her younger sister, aged nine, in a sex act.

Cimarron refused and said she would rather kill herself.

McCartney then put up a countdown clock, telling her “goodbye and good luck”.

Three minutes later, Cimarron was found by her nine-year-old sister who entered the room after she thought she heard a balloon pop.

She had shot herself in the head with the family’s legally-held firearm.

Cimarron was taken to hospital where she was pronounced dead.

Police have released the 911 call of the family calling for help.

On that fateful day in May 2018, Cimarron’s nine-year-old sister found her lying on the floor of her parents’ bedroom with a gun by her side.

Her family had no idea why she had taken her life and were unaware of the ordeal she had been subjected to.

Her mother Stephanie told investigators that she might have been unsure of her sexuality. Eighteen months later Cimarron’s father then took his own life.

However, years later the truth behind what had happened to Cimarron emerged.

Cimarron’s grandparents Peggy and Dale have taken part in an upcoming BBC documentary about McCartney where they remember their granddaughter but speak about their suffering.

They hope that raising awareness of what they went through will prevent other families suffering the same ordeal.

McCartney first appeared in court in Northern Ireland in late July 2019.

Police believe he targeted as many as 3,500 children on 64 devices between 2013 and 2019.

The court heard the harm McCartney caused was “unquantifiable” and he “degraded and humiliated” victims for his own sexual gratification.

Many of his child victims have never been identified, but all their lives have been changed forever.

Then in April 2021, just before McCartney was to be arraigned on some of the charges relating to the case, investigators discovered what had happened Cimarron.

In what is understood to be a legal first, he was charged with the manslaughter of Cimarron, which he pleaded guilty to.

McCartney eventually admitted about 185 charges involving about 70 child victims – aged between 10 and 16.

The Public Prosecution Service in Northern Ireland brought these forward as sample charges in order to produce an indictment the court could manage.

The court heard of the impact McCartney’s abuse had on his young victims – some said they have suffered flashbacks, shame, alopecia and trust issues.

Other girls now felt paralyzed when touched in any way by any man; that their childhoods had been stolen and some had suicidal thoughts.

The litany of McCartney’s crimes spanned continents.

BBC News NI has spoken to a man from New Zealand, we’ve called him Stephen (not his real name), about the abused suffered by his two girls, after McCartney struck up a friendship with his eldest daughter, then 12, on Snapchat.

The girl, we’ve called her Rebecca (not her real name), believed that she was talking to another girl.

That Rebecca believed to be a friendship grew over a few months. Then McCartney asked Rebecca for a nude photograph, which she sent.

“He then used that to manipulate and blackmail her into sending more photos, which ended up including our youngest daughter as well as part of the blackmail,” Stephen said.

“And then, in time, through her contact list on Snapchat he added Rebecca’s cousin as well, who was older at the time, and he then tried to threaten her with getting more photos.

“Thankfully, she was mature enough and smart enough to reach out to my wife, and then we went straight to the police from there.”

He said as soon as the first photo was sent, McCartney had power, adding that Rebecca was “playing by his rules” adding: “He preyed on her innocence.”

The father explained that his youngest daughter, who is two years younger, did not know what was happening.

“She just thought it was two sisters playing dress up and taking silly pictures, so she’s actually completely oblivious to it to this day.”

Stephen said McCartney’s offending has had a “profound impact” on his eldest daughter.

At the beginning of the year, she moved away for university but moved home after six weeks.

“I believe she missed out on opportunities because of trust issues. It’s something she’s going to deal with forever,” he said.

“We know she’s on this medication all the time, and the dark places that I’m sure her mind goes when she’s alone.”

Stephen said he and his wife have been devastated by what happened to their children but there was a silver lining in that they were able to play a “small part in bringing him [McCartney] to justice and preventing further victims”.

Further information and support for those affected by this story can visit the BBC Action Line.