Former police officer Lewis Edwards, who admitted more than 100 sexual offences against children, has been handed a life sentence.
He will serve a minimum of 12 years behind bars.
He was granted a reduction of one-third to his sentence due to his entering a guilty plea.
Sentences for other counts for which he pleaded guilty will be served concurrently.
Edwards, 24, carried out all but one of his offences while working as an officer for South Wales Police but was immediately suspended from duty upon his arrest and later resigned.
He used fake Snapchat accounts – posing as a 14-year-old boy – to groom more than 200 girls aged between 10 and 16 online.
Edwards asked scores of his victims for indecent images in school uniform and blackmailed many young girls – threatening to publish their photos or hurt their families to get them to cooperate.
The former officer, from Bridgend, had previously pleaded guilty to 22 counts of blackmail, 138 child sex offences and a further offence of refusing to disclose the password to a mobile phone and USB stick.
But this week he refused to appear at Cardiff Crown Court to hear his punishment.
Judge Tracey Lloyd-Clarke, the Recorder of Cardiff, told the court she could not force Lewis Edwards to attend court for his sentencing.
“He groomed his victims, psychologically manipulating them until he had gained control,” she said.
Describing his offences, she said: “The defendant had a pattern of behaviour. He made online contact with a girl.
“The defendant pretended to be a boy of a similar age. He groomed his victims psychologically, manipulating them until he had gained control.”
She added: “When his victims did not comply, he would threaten them until they did what they were told.”
The judge said Edwards continued his abuse even when the girls were crying and distressed.
“Even when told the victim was self-harming or suicidal, the defendant did not stop,” she said.
“He would threaten them until they did what they were told.”
One girl begged Edwards to stop demanding indecent images and videos of her.
“Please can you stop, I have my GCSE tomorrow morning, please, I’m begging you,” she told him.
The court heard how another of the victims told her father about what Edwards had been asking of her.
He took his daughter’s phone and sent Edwards a message saying, “This is [the girl’s] dad. Stop now. What you are doing is illegal.”
Edwards replied: “Lol.”
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The judge added, however, that he “did not use his position as a police officer in order to commit his offences”.
But she told the court that Edwards was the only person responsible for his crimes.
“It is important that everyone, particularly the victims and their families, understand that they have done nothing wrong,” she said.
“The blame and the responsibility for this event is the defendant’s and the defendant’s alone.”
She said Edwards’s sentence was “aggravated by the period of time over which these offences were committed, the number of victims, the number of images, almost all of which were moving images”.
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Judge Lloyd-Clarke said Edwards’s actions had caused “significant harm to the reputation of South Wales Police and the police in general”.
However, she acknowledged that were it for not the work of the force, Edwards would not have been brought to justice.
South Wales Police previously admitted the offences would “damage the public’s trust and confidence in policing”.
After sentencing, Assistant Chief Constable Danny Richards said there was “no place” on the force for “anyone who abuses the personal responsibility they hold as a police officer”.
“I understand there will be people asking how Edwards could have joined the police at the same time he was committing these terrible crimes,” he said.
“At the time of him joining South Wales Police his vetting was clear and there was nothing to indicate that he was involved in such abhorrent offences against children,” he added.
