By Mat Trewern
BBC Radio Manchester
Det Sgt Bob Willis has worked in the unit for six years
"I can remember the first images I saw and, every so often, they flash into your head."
For the past six years, Det Sgt Bob Willis has had to view horrific images of children being sexually abused as part of his work investigating Britain's paedophiles.
It's an aspect of his job that he still finds deeply disturbing.
"I get an image of the one I find the most horrifying. It's of an 18 month old baby," he said.
"The hardest thing is that, even though it's an 18 month old baby, you can see a hopelessness in the eyes."
DS Willis heads up a specialist team within Greater Manchester Police sexual crimes unit, the first of its kind in the UK dedicated to tracking down online child abuse.
BBC RADIO MANCHESTER
Radio Manchester's Mat Trewern reports on efforts by Gtr Manchester Police to track down online child abusers (15 - 19 March 2010)
It was here, in the 'viewing room' of their East Manchester offices looking out across the Pennines, that the team helped to uncover one of Britain's most notorious paedophile rings.
That investigation led to the arrest and conviction of Plymouth nursery worker, Vanessa George who took pictures of herself abusing toddlers on her mobile phone and another woman, Angela Allen.
The case shocked the country and even DS Willis was taken aback.
"It was completely unusual to have a nursery involved," he admitted.
"But that just gave us extra bite to make sure the inquiry was investigated and concluded as soon as possible," he said.
The internet has seen an explosion in the number of child abuse images but experts say the problem is moving away from pay-per-view websites.
Online file-sharing systems are fast becoming the most popular way of viewing and sharing abusive images.
Sifting through evidence at the Greater Manchester Police sexual crimes unit
But technology is also helping the police track paedophiles and find their young victims.
A new system created in the United States allows officers like Det Con Andy Pilling to search for known child abuse images and see exactly who has them on their computer.
Det Con Pilling said: "If I find someone from Manchester, I can get their address from the service providers and from there we can execute a warrant, so it's very quick.
"The key thing we're trying to find is the people who're abusing children. We can go to a house and find a victim of sexual abuse."
One woman who recognises the importance of this work more than most is Shy Keenan.
From the age of 4, she was raped and sexually assaulted by her step-father and 'sold' to other paedophiles on Merseyside.
Her abuse was photographed and filmed and is still being downloaded on the internet.
She's now an author and campaigner against child abuse and has nothing but praise for the detectives who investigate abusive images.
"To me they're the ultimate heroes. They will go into the darkest corners of this disgusting world and literally rescue living, breathing children."
"It was this this team at Greater Manchester Police that helped the country understand that we were children who not only need their protection but deserve it."
Det Sgt Bob Willis is due to retire next year from the job he loves but finds both challenging and troubling.
"You're well aware of the corrosive nature of what you're observing. Would I rather not be doing that? Yeah," he said.
"But the discomfort I feel is nothing in comparison to whatever is happening to that child. So you just deal with it and get on with it."
If you, or someone you know, are affected by issues raised in this report, you can contact the
The Child Exploitation and Online Protection (CEOP) Centre.