15 March 2012 Last updated at 07:21 ET

Suzanne Pilley's killer David Gilroy led a double life

By Lisa Summers & Angie Brown BBC Scotland

In May 2010 David Gilroy denied involvement in Ms Pilley's disappearance

Killer David Gilroy led a double life.

He deceived his wife and children about his turbulent affair with Suzanne Pilley, but when things turned sour he moved back home with them.

When Ms Pilley disappeared he was under intense scrutiny from the press, but he kept his cool and gave an astonishing interview outside his home in Silverknowes, Edinburgh.

However, the denials he made were false. He knew he was a killer, he knew he had murdered Ms Pilley.

Gilroy's mistake was to underestimate the huge electronic footprint that became a compelling body of evidence.

After analysing CCTV evidence, police had recreated a journey he made to Argyll and back three times.

They discovered Mr Gilroy had taken two hours longer than their average time each way.

And a comparison of fuel consumption suggested there were 124 miles unaccounted for.

Ms Pilley had been trying to end her relationship with Gilroy for good. He was desperate to keep it going.

However, pleading messages from him stopped abruptly as soon as she went missing on 4 May 2010.

When Ms Pilley made her final journey to work at Infrastructure Managers Ltd (IML) in Thistle Street on 4 May, she had just spent the night with a new man, Mark Brooks.

Gilroy could not accept that.

Scratches seen

He persuaded her to go to the office basement where he killed her.

He hid her body in a recess under a stairwell.

David Gilroy used make-up to cover scratches on his hands

Then he began his cover up.

Colleagues described him as seeming clammy, sweaty and with scratches on his neck and face. But he got his act together.

He made an excuse to go home and collect the car. He bought air freshners in Superdrug on Princes Street.

He used make-up to cover scratch marks on his hands.

He adjusted his diary to give him a reason to go to Argyll the following day.

Suspension damaged

As the court prosecution pointed out, Mr Gilroy, who was the one person with intimate knowledge of Ms Pilley, had gone on a journey of "no importance" the day after she had disappeared instead of "assisting the police inquiry".

Police found a recess under a stairwell at IML

He returned home that night and spent the evening with his family, all the time Ms Pilley's body was in the boot of his car.

He had made a journey to Lochgilphead, to check on a school his firm was overseeing.

However, he did not take a direct route and instead headed much further north.

He was logged at Tyndrum at 13:22, then Inveraray at 15:51 before arriving at Lochgilphead at 16:26.

Gilroy's car suspension was found by investigators to be badly damaged and it had vegetation stuck underneath.

They were convinced he had driven off road.

Detectives were certain he had detoured along the A83 to somewhere near the beauty spot, Rest and Be Thankful, with enough time to dispose of Ms Pilley's body.

A targeted, intensive search was organised for a weekend in August. The terrain was tough and ultimately Ms Pilley's body was not found.

As Gilroy faces a life sentence one question remains, where did he hide her body?

Ms Pilley's family hope that one day he will finally tell them the truth.