Gilroy always denied killing the 38-year old in May 2010 and attempting to defeat the ends of justice by concealing her body.
The "groundbreaking" police investigation into Suzanne's murder saw officers spend months viewing hours of CCTV footage taken in Edinburgh city centre and from roads in rural Argyll.
Detectives did not have a body and were dealing with an "unusual" and complex" case.
It started as a routine missing persons inquiry, with Miss Pilley's parents alerting officers their daughter had not turned up for work and could not be contacted.
Investigations soon led to the belief that Ms Pilley was dead. She was captured on CCTV getting off a bus at Jenners and going to a nearby supermarket on the morning of May 4, 2010. She was making a "routine journey to work" but was never seen again.
When police visited her home they found her passport, some cash and medication. There was nothing missing and nothing disturbed. Her family said there was nothing out of the ordinary.
The 38-year-old had a close relationship with her parents, contacting them daily. That stopped abruptly on the day she disappeared. None of her bank accounts were touched and her credit cards have never been used.
Prosecutors said these facts, brought together, demonstrated Suzanne was dead.
David Gilroy, 49, was first interviewed by police as a witness when it emerged the two had a relationship.
Police phoned him on his mobile the day after she was reported missing and he told them he was in Lochgilphead, Argyll, on business. He returned to Edinburgh late that night and gave a statement to officers.
Police said he was extremely co-operative and his statement ran to 59 pages after an 11-hour interview.
Officers noticed cuts on his hands, and Gilroy was asked to attend a forensic medical examination the next day. They believed he was covering the cuts with a "flesh-coloured substance", possibly make-up.
This was the "turning point" in his status, police said, but it took many hundreds more hours of police work to piece together the circumstantial case.
Specialist cadaver dogs brought in from South Yorkshire Police were used to search the basement and garage of the Thistle Street building where they both worked at Infrastructure Managers Limited. They also turned their attention to the boot of Gilroy's silver Vauxhall Vectra car.
The court heard areas of "interest" were found by the dog but no DNA or forensics linking him or Suzanne to the office areas were uncovered. No forensic trace of her in his boot was found.
Detective superintendent Gary Flannigan, the senior investigating officer, said: "The investigation into the murder of Suzanne Pilley has been groundbreaking and in many respects unique for Lothian and Borders Police.
"From the outset, we faced significant challenges and a routine missing persons inquiry quickly transformed into a murder investigation which relied heavily on information from the public."
He added: "The thing that makes it unusual and unique for our force is the fact that we didn't have a body, I think that's what changes the complexity for ourselves and makes it such a difficult case for the crown as well. Our use of the cadaver dog is certainly groundbreaking, our application of CCTV and the media appeal."
During the trial, the court heard 20 officers analysed just one second of CCTV footage. Hundreds of cameras across Argyll were looked at as police investigated the route Gilroy took to Lochgilphead on May 5, 2010.
Despite a significant response to a public appeal looking for information from witnesses who might have spotted a silver car and a a considerable number of weeks spent searching the areas where his car was seen on CCTV, her body was never found.
Mr Flannigan said: "We are confident that we have covered David Gilroy's movements from the moment he left IML on the Wednesday to the point he came to the police station. Clearly we've not looked in the right area or she's not been left there and there is always the possibility that she was placed somewhere else."
He added: "There's only one person who knows where Suzanne is, to our knowledge, and that's clearly David Gilroy."