Father Pleads Guilty to Posing as Teen Boy to Get Explicit Photos of His Teen Daughter

A New York father has pleaded guilty to federal pornography and exploitation crimes after he pretended to be a 15-year-old boy and tricked his own daughter into an online relationship in which she sent him explicit photos, PEOPLE confirms.

But the crimes didn't end in the cyber world, prosecutors say. Authorities believe the father allegedly began sexually abusing his then 14-year-old daughter for about a year until the girl told a school nurse, who then alerted authorities, Assistant U.S. Attorney Lisa Fletcher tells PEOPLE.

"It's especially diabolical," Fletcher says. "It's the ultimate betrayal of trust."

The man pleaded guilty Monday in U.S. District court in Syracuse, New York, to twelve counts including sexual exploitation of a child and receiving and distributing child pornography. He faces 15 to 250 years in prison at his July sentencing. He also faces sexual abuse and other charges in Herkimer County Court, District Attorney Jeffrey Carpenter tells PEOPLE.

'Boy' Threatened to Tell Teen Girl's Father

The plot began in October 2013 when the father made up a fake name and used photos of an unknown teen boy he found to set up Instagram and other online accounts and then began texting with the girl, Fletcher says.

The virtual relationship progressed to the point where they called each other boyfriend and girlfriend, even though they had never met in person. They engaged in sexually explicit chats, and he began asking her for nude photos, according to court documents.

Disturbed by the tone of the conversations, she tried to break it off with the person she thought was the 15-year-old boy. "All you talk about is sex sex and more sex. Honestly that's not what a relationship is about," she wrote to him, according to message excerpts contained in court filings.

But after he continued to badger her and threatened to tell her father about their chats as well as earlier photos of her in her underwear, she relented and sent him some explicit photos, adding, "Please don't make me send any more pictures. Please I beg you. I don't like it. I'm shaking really bad right now and I feel like I'm about to puke."

Says prosecutor Fletcher: "They call it 'sextortion.'" Fletcher added, "This would have been a crime even if he hadn't [allegedly] abused her."

On Thanksgiving Day, about a month after the texting began, according to Fletcher, the girl got a message she believed was from the boy's mother: It said the boy had killed himself.

Prosecutor: 'Probably the Most Unique Set of Facts I've Ever Seen'

Soon thereafter, prosecutors allege the man began molesting his daughter. "This case is probably the most unique set of facts I've ever seen, in terms of the length to which the cybercrimes went on, all in an effort to obtain sexually explicit photos," DA Carpenter tells PEOPLE.

While teens might think sexting can stay private, it often does not, he said. "Our youth needs to be educated that once an image of themselves goes on the Internet, it can never be destroyed," he said. "No one thinks of this, but it might be child pornography."

The man's attorney in the federal case did not return PEOPLE's call for comment. His lawyer in the state case, Cory Zennamo, said his client has pleaded not guilty on those state charges. "Just because someone pleads guilty in federal court doesn't mean he has a committed a crime in Herkimer County," he tells PEOPLE.

A trial on the state charges is scheduled for May.