A Northern Ireland man was sentenced Friday to a minimum of 20 years in prison after being found guilty by a U.K. court in what has been described as the biggest criminal “catfishing” case in the country. Alex McCartney, 26, had pleaded guilty earlier this year to a charge of manslaughter in a Northern Ireland court after a young American girl who was among the thousands of alleged victims he blackmailed online died by suicide. 

McCartney had admitted to a total of 185 charges involving 70 child victims in court — including blackmail, inciting a child to engage in sexual activity and producing and distributing indecent images of children. He was also held culpable for the death of 12-year-old Cimarron Thomas in West Virginia, according to the U.K.’s Press Association news agency. 

Thomas, who lived in West Virginia with her mother, father and siblings, died of suicide in May 2018.  During her online interactions with McCartney, authorties say he attempted to coerce her into sending graphic images involving a younger sibling.

McCartney was already under investigation at the time, and was about to face charges from British investigators when authorities discovered Cimarron’s identity and the circumstances of her death, CBS News’ partner network BBC News reported Friday.  

Thomas’ father, a U.S. Army veteran, died by suicide 18 months after his daughter, not knowing any of the circumstances behind Cimarron’s death.

Jim Gamble, a former senior British police officer specializing in child safety, told BBC News that it was a “shocking case.”  

“The sheer scale of it and the horrific nature of the harm inflicted on these young girls makes it one of the worst I’ve ever seen,” Gamble said, adding: “Don’t watch this and think this happens very rarely.”

Detective Chief Superintendent Eamonn Corrigan of the Police Service of Northern Ireland’s Crime Operations Department issued a statement Friday, calling McCartney “nothing but a disgusting child predator who was posing as young girls online to groom, manipulate and sexually abuse his victims, as young as four, to satisfy his own sexual perversions and that of other online child sexual offenders.”

McCartney’s crimes occurred between 2014 and 2019, when he’s believed by police to have targeted about 3,500 victims, mostly via Snapchat, all over the world, including in Australia, New Zealand and the U.S., according to the Press Association. The case against him in the Belfast Crown Court focused on 70 child victims, including Thomas.

There was no immediate response to Friday’s verdict against McCartney from Snapchat. The social messaging app was accused in September of having features that make it a favored platform of sexual criminals targeting children, in a lawsuit filed by New Mexico against its parent company, Snap Inc.

An undercover investigation by the state found Snapchat has crafted “an environment where predators can easily target children through sextortion schemes and other forms of sexual abuse,” Attorney General Raúl Torrez said in a news release.

In a statement responding to the New Mexico case, Snap said the app was designed “as a place to communicate with a close circle of friends, with built-in safety guardrails,” and it said there were “deliberate design choices to make it difficult for strangers to discover minors on our service.”

“We continue to evolve our safety mechanisms and policies, from leveraging advanced technology to detect and block certain activity, to prohibiting friending from suspicious accounts, to working alongside law enforcement and government agencies, among so much more,” the company said, adding that it continued to work with “industry, government, and law enforcement to exchange information and concept stronger defenses.”