The eight convicted members of the paedophile network are (top, left to right) Colin Slaven, Craig Boath, James Rennie, John Milligan, (bottom, left to right) John Murphy, Neil Strachan, Ross Webber and Neil Campbell
By Lisa Summers
BBC Scotland reporter
The two men at the centre of Scotland's biggest paedophile network shared a deeply disturbing interest in the sexual abuse of children.
They chose to pursue that interest online.
Both Neil Strachan and James Rennie had established close friendships with families in order to become close to their young children.
Both deliberately manipulated those friendships, betraying the families in an unimaginable way.
They took pictures and made short films of themselves abusing the children, then posted them on the internet for other paedophiles to see.
In the ping of an e-mail those images of real, innocent children were transported to the web - and there they will remain, forever.
For the families involved that is one of the most difficult realisations of the past two years.
The sentencing of the two perpetrators may give them some kind of closure, some means to move on, but other may still be passing on the images of their children being abused.
As the father of Rennie's victim, Child F, told me: "The genie is out of the bottle, and you can never put it back in."
The police trail to Strachan and Rennie began with one simple mistake. Strachan left a folder called "young boys" on his work computer.
Detectives seized huge amounts of abuse images
It was sent for repair and a computer apprentice discovered the file on the removable hard drive.
That discovery was made in August 2007. In October of that year, Lothian and Borders Police set up Operation Algebra.
It was to become the biggest police investigation of its kind in Scotland.
Officers very quickly realised that Neil Strachan was known to them. He already had two previous convictions for sexual abuse and was on the sex offenders register.
He was also HIV positive. But he had evaded authorities and befriended a couple and their two young children.
After arresting Strachan and his 23-year-old partner, Colin Slaven, computer forensic specialists began to trawl through recovered internet traffic, looking for information on any other possible paedophiles.
The lead investigating officer, Det Insp Stuart Hood, soon became suspicious of one e-mail address in particular.
Strachan was in regular correspondence with somebody who owned the Hotmail account kplover.
What made police particularly concerned was that the person behind the kplover address appeared to be offering a child for abuse.
Police had to go to the authorities in America to put a stop on the kplover account, which was managed by Microsoft in California.
In the first instance police could only trace the account to the Meadowbank area of Edinburgh.
They also realised it had been accessed from the offices of LGBT Youth Scotland in Leith.
Det Insp Hood called in the expertise of the Online Child Protection Agency and an undercover surveillance expert.
He discovered that the owner of the kplover address had been using unsecured wi-fi accounts in an attempt to avoid detection.
By mapping where the routers crossed paths he was able to pinpoint a flat on Marionville Road that had access to two wi-fi accounts which were not password protected. The flat belonged to James Rennie.
Officers used sophisticated computer software to trace Rennie
The arrest of Rennie in December 2007 was a significant breakthrough for police.
A search of his flat revealed a hidden recess in an airing cupboard that contained thumb drives, DVDs and a considerable amount of child abuse imagery.
But it was on examination of his recovered internet files that police realised they had intercepted a massive paedophile network.
Rennie had been in touch with paedophiles across the world. Among them were a convicted rapist in America and an unknown paedophile in the Netherlands.
The information gleaned from his computer was to lead to the arrest of another five men in Scotland - John Milligan, Ross Webber, Craig Boath, Neil Campbell and John Murphy.
They were sentenced in June along with Slaven. But the information uncovered by forensic experts has initiated around 100 fresh police investigations in the UK and overseas.
The court case began on 2 March. It was to last 10 weeks, making it one of the longest and most significant in Scottish legal history.
It was the first time prosecutors had managed to successfully prove that the men in a paedophile network had conspired to gain access to children to abuse.
While Strachan and Rennie were convicted of physically abusing children, the evidence presented, largely through transcripts of online conversations, was enough to prove to the jury that others intended to abuse if the opportunity presented itself.
The sentencing of Strachan and Rennie on Thursday brings to a formal end the biggest police operation of its kind.
But for the families at the centre of it, they may never know the full extent of what these men did to their children.
All they can do is find the strength to move on and provide a secure, loving environment for their children and be there to answer questions in the future.
Both the families involved in this case have shared their story with BBC Scotland because they believe that we don't realise the full horror of child abuse.
The BBC Scotland investigation Who Can You Trust? will be broadcast on BBC 1 Scotland at 2335 GMT on Thursday.