Police are carrying out an underwater search for a mother who vanished in 1997 shortly before she was due to give evidence in a paedophile court case.
An underwater search is being carried out for Allison McGarrigle
Detectives believe Allison McGarrigle, from Rothesay on the Isle of Bute, was probably murdered and dumped at sea.
The operation will be assisted by Police National Search Adviser Mark Harrison and a sonar equipment expert.
They will survey an area of the Firth of Clyde between Largs and Millport ahead of a full hunt in the spring.
The advanced equipment on board the search vessel is of the same type used in the US to find pieces of the Columbia space shuttle which broke up as it re-entered the earth's atmosphere.
Detective Superintendent Stephen Heath, who is leading the investigation, said: "This equipment x-rays the seabed and sends up a picture live on a screen.
"In terms of remains of a body, which sadly is what we are looking for, that can be slightly tricky. I don't think it's been used before in Scotland."
He added: "The experts have been deployed worldwide, so it is a first in this kind of search. We're trying to focus in on a particular area of sea which has become very interesting for us.
"The reason we have re-launched this inquiry and have made significant developments in the last three or four weeks is because technology has changed and loyalties change as well."
The detective continued: "We have new leads. We wouldn't go on an exercise as technical as this without having assessed that it is achievable.
"It's a very sad story. A family have lost their mother and they have had no settlement to this for seven or eight years."
Det Supt Heath continued: "I think sadly she's been brutally murdered and she's been dumped in the sea in some kind of container and that's really what we are looking for."
Allison McGarrigle's son Robert has appealed for help
Mrs McGarrigle's son, Robert, 21, said last month he would do whatever he could to help police find her body.
He said: "Although seven years have passed since she disappeared, I have never stopped wondering what happened to her.
"Police now believe she is dead and it would help myself and the rest of my family if we were given the chance to lay her to rest.
"I would urge anyone who knows what happened to my mother or has any information that may assist in their inquiries to contact them."
Mrs McGarrigle, 40, was due to give evidence against two men who were later convicted of indecent assault and drug offences.
The mother-of-three was last seen by her family in June 1997 in the Largs area, where she had been lodging with two cousins.
No charges have been brought in connection with her disappearance.