Prosecutors say 26-year-old Alexander McCartney, from Newry in Northern Ireland, pretended to be a teenage girl and carried out catfishing attacks on 3500 female victims he contacted on platforms including Snapchat.
Catfishing is using a fake online identity to deceive victims. Authorities said McCartney encouraged his victims to send intimate photos or engage in sex acts, then extorted them by threatening to share the images.
A 12-year-old in West Virginia killed herself in May 2018 during an online chat with McCartney as he demanded sex acts.
The victim's father died by suicide 18 months later.
Prosecutors said they believe this is the first time someone has been convicted of manslaughter in a case where victim and perpetrator never met.
"Working closely with police, the prosecution team was able to establish to the criminal standard that McCartney's actions had caused the girl's death and he had a case to answer for manslaughter," said Catherine Kieran, acting Head of the Northern Ireland Public Prosecution Service Serious Crime Unit.
Police have identified victims in 30 countries, including Australia, New Zealand and the United States.
McCartney, who carried out his crimes from the bedroom of his childhood home, pleaded guilty to 185 charges involving 70 children, including the manslaughter charge.
At Belfast Crown Court, judge John O'Hara sentenced him to life with no chance of parole for 20 years.
"To my knowledge there has not been a case such as the present where a defendant has used social media on an industrial scale to inflict such terrible and catastrophic damage," the judge said.
Detective Chief Superintendent Eamonn Corrigan of the Police Service of Northern Ireland said outside court that McCartney was a "relentless and cruel" paedophile.
"We cannot underestimate the devastation that he has caused and the childhoods he has stolen," the officer said.
"There was nothing that was going to stop him, apart from putting him in jail."
Child sexual abuse that happens online is just as serious as abuse that happens in person 🖥�💻📱 It can deeply affect a child's well-being, and it's something we need to address directly. Help create a safer online world for our children and young people: — eSafety Commissioner (@eSafetyOffice) https://t.co/AXkpu4gd9kSeptember 26, 2024
A New Zealand father has said he will never forgive McCartney for abusing his two young daughters.
Bob, who only wanted to be referred to by his first name, said his family has been left devastated after the online abuse.
The father said his oldest daughter was just 12 when she was contacted from the other side of the world by McCartney in December 2017.
"He befriended my oldest daughter on Snapchat, it was just a random connection," Bob told the PA news agency.
Then over a period of a few months he built trust with her, she believed she was talking to a female, not a male, he said.
The father said he then elicited for her to pose for a nude photo, which she sent.
"Once he had that, he had the power and it was a case of playing by his rules," Bob said.
"He manipulated and blackmailed her into sending more pictures which included my younger daughter, photos of her ended up being sent as well."
with PA
