The garden in Irvine Drive, Margate, was scanned by GPR

Crucial to their search - which has uncovered the bodies of two missing teenagers - has been a sophisticated radar system.

Their remains may have lain undiscovered for more than a decade and a half.

But when detectives looking for Vicky Hamilton and Dinah McNicol - who were aged 15 and 18 when they vanished in 1991 - turned their attention to a property in Irvine Drive, Margate, officers knew what would lead them quickest to any burial sites.

Ground-penetrating radar (GPR) allows investigators to build up a picture of what objects may be buried underground - without having to dig up any earth.

And sure enough, the system led police to the bodies of both girls at the property, which was formerly occupied by a man called Peter Tobin.

'Avoid digging'

This is not the first time that forensic teams have used GPR in such cases.

It's about creating a more efficient search Jon Dittmar ERA Technology

Jon Dittmar is an engineer with ERA Technology - the company brought in by police to look for bodies at the house of Fred and Rose West in Cromwell Road, Gloucester, in 1994.

In the mid-1990s, he worked with Belgian police hunting for victims of the paedophile and serial killer Marc Dutroux.

He explains GPR uses radar signals to indicate where the ground could have been disturbed.

"You don't get a picture of a skull staring back up at you," he says.

"It's about creating a more efficient search, one that shows you where you should be digging.

"If you can avoid digging up concrete or foundations, so much the better - you've got to put it all back again and that's expensive."

GPR works by sending a series of electrical pulses into the ground.

The signals that bounce back allow engineers to map out where objects, cracks and voids are located below the surface.

They allow teams to focus their digging efforts on specific locations.

'Impressive array'

Peter Barker is managing director of Stratascan, a Worcester-based geophysics company that also provides GPR services to police forces.

He says the system is much more thorough than other types of probes.

"You can work through hard surfaces with it, through patios and floors," he says.

"If you grid the site methodically, you can get a very impressive array of data."

The technique is not only used to help police, he says. Archaeologists and construction engineers also find it invaluable.