A 21-year-old Saskatchewan man is facing a penitentiary sentence in a child pornography case described by a veteran Crown prosecutor as possibly the most egregious in provincial history.

Shane Dale Pattison, who lives with his parents in the small town of Marshall near Lloydminster, pleaded guilty last November to 53 charges including possession, distribution and production of child pornography.

His sentencing hearing began Monday in Saskatoon Court of Queen's Bench and is expected to continue on June 15.

Speaking to reporters outside court, Crown prosecutor Mike Segu said Pattison is "the worst offender I have ever seen" in 12 years of prosecuting child exploitation cases.

Pattison collected and shared more than 4,500 illegal photos and videos, most of them depicting extreme sexual abuse of female children under the age of five, over a two-year period starting in the fall of 2009.

His digital collection of atrocities included a highly detailed 170-page instruction manual on how to sexually abuse children from infancy and train them to keep it secret.

"It is perhaps the most disturbingly complete manual I have ever encountered," Segu told Justice Mona Dovell.

Pattison used several free Internet file-sharing programs, as well as anonymous email accounts and two false Facebook profiles, to establish a network of contacts with hundreds of like-minded people all over the world - including frequent online chats and file exchanges with an Idaho man who was actively abusing his own four-year-old niece.

As a result of investigations into Pattison's activities by the Saskatoon police Internet child exploitation (ICE) unit, the Idaho girl was rescued and her uncle is now serving 15 years behind bars, Segu told court. In addition, two other little girls in the state of Georgia and one child in British Columbia were also rescued.

About 200 of Pattison's online contacts are now also under investigation by police in numerous jurisdictions, court heard.

During one chat with the Idaho man, Pattison said that he and his girlfriend were trying to have a baby and that he intended to begin using the infant "for a sex toy" as soon as it was born.

Pattison's girlfriend did eventually get pregnant, giving birth to his child seven months ago. Segu told court Social Services initially had some involvement, but after a custody hearing she was allowed to keep the baby, in spite of the fact she still has ongoing contact with Pattison. He is not being held behind bars while his sentence is pending.

Amid the mountain of horrifying evidence recovered from Pattison's laptop after his home was searched in November 2010, police found Internet chats in which he falsely bragged to others about having sexually tortured, mutilated and murdered more than one small child.

They also found records of his web browsing history that showed he was actively searching for babysitting jobs in Lloydminster and Edmonton through web-based classified ads on Kijiji, Craigslist and SOSsitter, court heard.

Pattison's Facebook activity - openly trading child porn photos and videos on two profiles that were left open for viewing by anyone - prompted 31 public complaints to the U.S.-based National Centre for Missing and Exploited Children, court heard.

In a videotaped interview with police after his arrest, Pattison said he was "addicted" to child porn and had made several failed attempts to quit collecting it.

"I wanted to stop, but I don't know how," he told an investigator.

Pattison told police his girlfriend had previously discovered his habit, but had declined his invitation to look at child porn with him, saying she was sexually assaulted by an adult during her own childhood.

He also admitted to police that he would likely commit a sexual assault if left alone with a child, Segu noted.

Defence lawyer Brian Pfefferle told court Pattison was diagnosed with bi-polar disorder in 2008 and is taking prescription medication for it.

Pfefferle said he intends to argue that Pattison's mental condition was a "contributory factor" in his crimes.