The head of a specialist dive squad searching for missing mum Nicola Bulley says he fears possible third party involvement.
Private underwater expert Peter Faulding spoke out after his team joined the search effort for the 45-year-old using sonar technology in the River Wyre in Lancashire.
He said he has spoken to her partner Paul Ansell and he was "distraught".
During a phone chat last night, Mr Faulding said he asked Paul if Nicola "had any stalkers or enemies or anything like that but he's completely baffled as well".
The expert said he feels like he is searching for an "invisible person" since he was drafted in by police yesterday.
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He told Good Morning Britain: "I personally think if I rule this stretch of river out today where we're working I don't think she's here, I think there's probably a third party involved."
Mr Faulding told the Mirror this morning his team are focusing on what he considers the "hot zone" in and around where she disappeared.
He said they started yesterday at the weir around 200 metres away and continued for around three miles to rule that section out.
"We’ll continue, we are going to do a really careful survey in the hot zone, where Nicola went missing originally," Mr Faulding explained.
"Where we were searching yesterday wasn’t what I called the hot zone. This is the hot zone, where we are searching today."
He went on to add: "If she’s here I’m confident we’ll find her in this section of the river. If she’s here. If I don’t get any targets today then she’s not in this part of the river. She’s not here.
"I don’t think she’s drifted far, that’s my personal opinion. The tide would have pushed her in."
Mum-of-two Nicola vanished on January 27, sparking a major search and rescue mission led by police, who have been assisted by the fire brigade, coast guard and the RNLI.
Police divers, sniffer dogs, drones and helicopters have also been involved in the search but they have still been unable to find the mum-of-two.
A private team of divers led by Mr Faulding, a leading confined space rescue and forensic search specialist, search the water where police believe she fell.
He and his team of divers from Specialist Group International (SGI) will be searching the river free of charge for the next four days.
But Mr Faulding, who has worked on a number of high-profile missing persons and “no body” murder investigations, has been left baffled by the lack of clues in the search.
However he is "holding out hope" that she is alive and safe somewhere.
Mr Faulding said: "I'm baffled and we're all baffled by this case because the police divers searched this area in front of the bench the same day she went missing.
"I would expect a body to be at the bottom of the river.
"In my experience, it would literally be in the river in front of the bench - that's where you would normally find it.
"It's mad and it's just very odd if I'm honest.
"But I think we need to hold out hope that she's alive somewhere as she's just disappeared off the face of the earth.
"We just don't know, we're looking for an invisible person at the moment and we've got no idea.
"I think we need to do what we can, the police are doing a great job and we're all doing a hard job."
Mr Faulding said he updated Paul, Nicola's partner and the dad of their two daughters, which left him "distraught".
And he called for social media users speculating on the case to "leave the family alone".
He said: "I had a half an hour conversation with Paul last night to update him and he's distraught.
"There's so much horrible things that have been going on, I feel so sorry for the man.
"He's getting constant flack all the time and it's not fair.
"The family just need to be left alone and everyone needs to let us do our job."
He also said that the only clues the police have about the case are her mobile phone and her dog Willow's harness, which were found minutes after she was last seen.
Mr Faulding said: "The only clue the police have got is just the mobile phone and the dog harness. That's it - there's nothing.
"I've worked on hundreds of cases and I've never seen anything like this as we would have expected to have found her by now."
His comments come after a large police presence was spotted on the Shard Bridge which crosses the River Wyre, five miles down from where Nicola disappeared.
One resident posted on social media: "Police presence on Shard Bridge including drones.
"Looking for something."
