A crime scene investigator who helped police nail serial killer Peter Tobin has revealed the major clue which led to a key discovery about one of his victims.

Peter Faulding, a leading forensic search expert, was enlisted by detectives to scour Tobin’s West Lothian home after they discovered that he was living there when Vicky Hamilton ­disappeared in February 1991.

Peter told the Daily Record: “Tobin was charged with killing Angelika Kluk in Glasgow in September 2006 and it was during that inquiry, Operation Anagram, that it was discovered Tobin had actually been living in a house in Robertson Avenue, Bathgate, when Vicky disappeared.

“The investigators had been building up a picture of Tobin’s life. Meanwhile, a cold case review had been set up by Lothian and Borders Police called Operation Mahogany in spring 2006.

“When they realised the link with Tobin, they gave Lothian and Borders the breakthrough they needed to search Robertson Avenue and that’s where I was involved.

“We spent a week ripping the garden and house apart. We didn’t realise at the time the significance of it all. We were just doing our jobs but we knew police had to keep their interest in Tobin secret for fear of prejudicing the Glasgow case.

“They already had a DNA link on Vicky’s purse that matched Tobin’s son so the house in Bathgate was an area of massive interest.”

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But it would be a suspiciously large rockery in the garden that led the team to the pit where the 15-year-old's body had been buried before she was moved by Tobin when he moved house.

Peter said: “We’d already ripped apart the garden and discovered signs the ground had been disturbed under a giant rockery in the back garden and that heightened for us the possibility that we would find something in the house.”

Vicky was last seen at a bus stop in Bathgate, and Tobin, 75, was eventually convicted of her murder in 2008 following an investigation which led to the discovery of Vicky’s body in a garden in Margate, Kent.

The body of 18-year-old Dinah McNicol was also found buried there.

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Peter, a former Parachute Regiment reservist, searched the house with a team from his company, Specialist Group ­International (SGI), which uses cutting-edge technology.

He said: “We didn’t know much about Peter Tobin at that point. Our brief was to go in and strip the house with the intention of hopefully finding some evidence that Vicky Hamilton had been in there and perhaps still was.

“The first thing that caught my eye was the huge rockery in the back garden. It was an unusual feature. We removed it and police brought the cadaver dogs in.

“Our radar had shown the ground had been disturbed. We excavated the whole garden and suspected Vicky had been placed under there for a number of months before being moved.”

Next, the team moved inside and began systematically tearing apart every room where they found more evidence linking Tobin to the house and the crimes.

Peter said: “Our radar also detected disturbance under the kitchen floor so that was torn up but it turned out to be natural subsidence.

“When we got into the attic there were several old belongings from Tobin that had stayed there for 16 years.

“In among the lagging and a corner of the loft, we discovered a knife. It had either fallen or been placed between an end joist next to a supporting wall, in a gap about 6cm wide and 20cm deep."

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Peter likened the discovery to a 'eureka' moment in the case that eventually convicted Tobin, who is serving a life sentence in HM Prison Edinburgh. 

He said: “It was sent for analysis and came back pretty quickly that there was traces of tissue belonging to Vicky on it. We were elated because that linked Tobin to Vicky.

“It really was a eureka moment because we felt we were close to discovering what happened to Vicky. Her body was found just a few months later 500 miles away.

“He may look like a frail old man but he is a dangerous predator who has caused misery for so many people. I feel nothing but hatred for the pain he has caused.”