A Northern Ireland man was sentenced to life in prison on Friday for mass online sexual abuse and blackmail of young girls around the world, in an incident police said led to a 12-year-old American girl and her father take life

Belfast Crown Court heard that 26-year-old computer science student Alexander McCartney, who operates from the bedroom of his family home, groomed victims on messaging sites including Snapchat and Instagram, tricking them into thinking they were chatting online with a teenage girl of the same age.

He would then encourage them to send indecent images or engage in sexual activity via a webcam or mobile phone, which he would then share online with others and use to threaten children. He regularly assumed the identity of previous girls he had targeted and sometimes forced his victims to implicate siblings as young as three in the abuse.

The allegations related to 70 victims from countries including the United Kingdom, the United States, Ireland and Australia, but police in Northern Ireland said it was a small fraction of about 3,500 victims believed to have been targeted in about 30 countries.

“His offending was on an industrial scale … his depravity knew no bounds,” Detective Chief Commissioner Eamonn Corrigan told reporters from the Police Service of Northern Ireland after sentencing.

One of his victims, 12-year-old Cimarron Thomas from West Virginia, took her own life in 2018 with her father’s gun while online with McCartney and was found by her nine-year-old sister, a heard the court. Their father took his own life after her death, police said.

“We will never forgive and we will never forget the horrific things this predator did,” the father of one of McCartney’s New Zealand victims was quoted as saying in a police statement.

McCartney, who Judge John O’Hara told the court was guilty of “sadism and depravity”, will be eligible for release in 2039.

McCartney sat with his head down as O’Hara listed his crimes and stood up with his eyes closed when the sentence was announced. He was taken away in handcuffs. He pleaded guilty to all charges.

Police said during the investigation they seized 64 devices with hundreds of thousands of indecent photos and videos and the fake digital accounts used by McCartney.