An underwater forensics expert believes missing mum Nicola Bulley's phone may have been left by the river as decoy.
Specialist Group International (SGI) were drafted in by police yesterday to help trawl the River Wyre for the dog walker.
Founder Peter Faulding, who was yesterday pictured operating the firm's high-tech side scan sonar from a boat, said he is "truly baffled" by the case.
He admits there are many confusing elements, and prior to joining the search yesterday told the Mirror he expected SGI's equipment to find Nicola in under an hour if she was in fact in the river.
Despite finding little in the way of clues so far, he has since said he does believe she went into the water and he's set to head back out later today.
Mr Faulding said all the police have to go on right now is Nicola's phone, which was left on a bench overlooking where investigators suggest she may have fallen in.
Her dog was found wandering alone nearby, with her harness and lead removed.
Speaking to TalkTV last night, Mr Faulding said: "After 25 years of doing this kind of work, after hundreds of cases, I am well and truly baffled.
"When people drown they generally go down where they are. We normally find them within five to ten metres of where they went down even after a few days.
"This is the most baffling case that I have ever worked on. The police have nothing to go on.
"All they have is a mobile phone at the moment and they said it could possibly be a decoy."
Nicola had dropped her two daughters at school in St Michaels on Wyre on the morning of January 27 and then took springer spaniel Willow for a walk along a river towpath.
She was seen for a final time by a witness at around 9.10am, having logged into a work conference call at just after the hour.
At 9.33am another dog walker found her phone on a bench, with a distressed Willow nearby.
Police subsequently launched a major search operation, which is now entering its 12th day.
Last week Superintendent Sally Riley said investigators were working under the main assumption that she accidentally fell into the river. However, she admitted there was no clear evidence of that.
Nicola's boyfriend Paul Ansell released another appeal and thanked Mr Faulding and his team for the efforts.
"I have two little girls who miss their mummy desperately and who need her back," he said.
"This has been such a tough time for the girls especially but also for me and all of Nicola's family and friends, as well as the wider community and I want to thank them for their love and support.
"We are also really grateful to Peter and his team from SGI for coming up and helping support the work of Lancashire Police as they continue their investigation.
"If anyone has any information which could help find Nicola, I urge them to get in touch with the police and help us provide the answers we all so badly need."
