A man who authorities say amassed the largest stockpile of child pornography in Pennsylvania history has been sentenced to 100 years in federal prison.

Lawrence “Larry” Jamieson Jr., 59, of Malvern, was sentenced last week on charges related to the sexual abuse of a young girl, the manufacture of hundreds of sexually explicit videos and photos of the abuse and his collection of child porn that he downloaded from the internet.

The U.S. attorney for Eastern Pennsylvania said Jamieson's collection, which he began 15 years ago, contained "some of the most demented images imaginable" of young children enduring sexual abuse.

"Jamieson is the worst of the worst type of criminal -- a child predator who derives satisfaction from abusing society's must vulnerable members," U.S. Attorney William McSwain said in a statement. "The details in this case are horrific. This defendant amassed a collection of child pornography that exceeded 14.4 million images, reportedly the largest collection in Pennsylvania.

“And on top of that, he concocted and carried out a plan to sexually abuse a child within his care -- someone he knew was susceptible to his influence. For more than 18 months, Jamieson and his co-defendant repeatedly lied to his victim and engaged in an unconscionable course of sexual abuse and exploitation.”

McSwain’s staff reported that Jamieson targeted a girl who he knew was diagnosed as being on the autism spectrum. She also has other learning disabilities and mental health issues.

"He targeted this underage girl by first recruiting another adult male to pose as a teenaged boy so that they could dupe the victim into believing he was her boyfriend and gain her trust," McSwain said in a news release. "The 'boyfriend' then engaged her in sexual activity, photographed and videotaped her, and distributed the videos and images back to Jamieson. Her images were also distributed out to others over the internet."

The girl was 15 and 16 at the time of the abuse.

The Daily Local News in Exton reported that the sexual assault victim is now 19 and living with her mother. She has trouble eating and sleeping and cannot forget the images of her that were distributed over the internet.

"She is completely broken," Assistant U.S. Attorney Michelle Rotella told the newspaper. "She just feels like she can't move forward."

Jamieson, who pleaded guilty on the charges in September 2017, apologized to the court, the girl and her mother and to his own family during his sentencing hearing, the Daily Local News reported. He is part of a well-known and respected family in Philadelphia's Main Line community.

His late father, Larry Jamieson Sr., was a successful insurance agent and once served as a member of Downingtown Borough Council. Jamieson's mother owns a well-known interior design business in Haverford, the newspaper reported.

WPVI in Philadelphia reported that Jamieson and his accomplice, John Brown, of Norristown, were arrested in August 2016 after the Willistown Police Department received a complaint about the sexual abuse. Police officials said at the time that Jamieson and Brown convinced the victim that Brown, 23, was a 17-year-old cyber school student.

Brown changed his appearance to look younger, the news station said. Once he began abusing the girl, Jamieson also joined in.

"Even after decades of serving in law enforcement, the scope and nature of these crimes are staggering," Willistown Township Police Chief John Narcise said in a statement obtained by the news station. "I have never seen as large a trove of child pornography in the history of Chester County, and the rest of the conduct is unspeakable. I do not know what kind of a depraved mind could possibly enjoy this sickening abuse of innocent children."

Rotella said prosecutors are pleased with Jamieson’s sentence.

"He will never be getting out (of prison) again," she told the Daily Local News. "He is just a true predator and, if he had ever been released, it is a virtual certainty that he would have victimized someone else."

Brown, now 27, has also pleaded guilty to similar charges and is scheduled for sentencing later this year, the newspaper reported.