Alexander McCartney: Catfish killer brought down by one phone call

As the investigation spread across the globe, Ms Kierans said prosecutors realised McCartney had been "very assiduous about saving the images".

"He would also save the map on Snapchat of where the child was in some cases, and that then enabled police to locate the children.”

His arraignment in 2021 was delayed as police discovered the suicide of a little girl in West Virginia, USA.

“From the beginning, the level of abuse was so horrific that we were fearful that when these children were identified, would they be okay?” Ms Kierans said.

“Unfortunately, our worst fears were realised when we discovered, some way in, that one of the little girls had taken her own life.

“Working closely with the American authorities, we were able to prove that this child took her own life during the abuse, when she was still online with McCartney.

"At that point, the death of the child was so intrinsically linked to the abuse that we felt we had a strong case to say that he killed her."

That little girl was 12-year-old Cimarron Thomas who, in 2018, shot herself while McCartney was abusing her.

McCartney was charged with her manslaughter.

Ms Kierans said it is believed to be the first time an abuser anywhere in the world has been held accountable for manslaughter where the victim and perpetrator have never met in person.

Such was the magnitude of the case that prosecutors had to be judicious with the charges.

“We couldn't put 3,000 charges on the indictment,” Ms Kierans said.

“In the end, there were about 200 charges [relating to around 70 victims] which is probably one of the largest indictments that we've seen in Northern Ireland."