An online predator from Northern Ireland who drove one of his catfish victims in the US to take her own life is set to be sentenced.

Alexander McCartney, 26, has admitted 185 charges involving 70 children, although a court has previously been told that the real number of victims is much higher.

McCartney, who posed as a young girl to befriend other girls on Snapchat before blackmailing them, is believed to be the UK’s most prolific catfish offender with victims identified across the world.

Twelve-year-old Cimarron Thomas from West Virginia in the US took her own life in May 2018 rather than comply with McCartney’s demands for her to involve her younger sister in sex acts.

Laganside court
McCartney will be sentenced at Belfast Crown Court (Liam McBurney/PA)

Eighteen months later, her heartbroken father Ben Thomas also died by suicide.

McCartney has pleaded guilty to manslaughter relating to Cimarron’s death.

He also admitted 59 counts of blackmail, dozens of charges related to making and distributing indecent photographs and scores of charges of inciting children to engage in sexual activity.

The offences cover a period from 2014 to 2019 with victims being identified all over the world, including Australia, New Zealand and the US.

McCartney used his technical knowledge as a computer science student to carry out his crimes.

His offending was carried out from the bedroom of his childhood home.

McCartney, originally from Lissummon Road outside Newry, has been on remand in Maghaberry Prison since 2019.

He posed on the Snapchat social media platform as a teenage girl and befriended vulnerable girls aged between 10 and 16 who were gay or exploring their sexuality.

Once he had secured a picture from his victims, he would then reveal the “catfish” and blackmailed them into taking part in sex acts.

In some instances, he demanded his victims involve younger siblings.

McCartney told one girl he would get people to go to her house to rape her if she did not comply with his demands.

McCartney was arrested several times between 2016 and 2019 but continued to offend despite bail conditions until he was remanded in custody.

At a pre-sentence hearing last week, a prosecuting barrister said McCartney had degraded and humiliated his victims, stating that the harm caused to them was “unquantifiable”.

The barrister also read out parts of a victim impact statement which had been provided to the court by the grandparents of Cimarron Thomas.

The statement said: “Our lives will never be the same.

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

“We have been robbed of those memories. Our lives have changed forever.”

Mr Justice O’Hara will sentence McCartney on Friday at Belfast Crown Court.