Police will be looking into three theories while trying to find missing Nicola Bulley, a retired detective has told the Mirror.
The mortgage adviser, 45, disappeared last Friday morning while walking her brown spaniel Willow along the River Wyre in the tight-knit village of St Michael's-on-Wyre in Lancashire.
Police have stressed that they don't think there is any third-party involvement. However, family and close friends have told the Mirror they fear someone has taken her.
The alarm was raised when someone recognised Nicola's dog running loose and found its harness and the mum's mobile phone nearby.
They phoned her daughters' school who then contacted her partner Paul Ansell.
A massive search has been launched and is still continuing along the river where Nicola was last seen. Divers have been seen going underwater and boats have trawled the surface.
Julie Mackay, a retired Detective Superintendent who previously solved a 32-year-old murder, has told the Mirror that she thinks the police will be looking into three theories while trying to solve this "unusual case".
She said: "It is an unusual case. Naturally, if someone had been gone that long then something bad has happened to her.
"Whether that is criminal or accidental will be determined at a later date.
"The police will have been focusing on examining that scene to understand what's happened. They will have a number of working hypotheses.
"One is that is would have gone off of her own volition, but that is unlikely because she seemed happy at home.
"Another one is that she's a misadventure, like an accident, because she was so close to the river and fell in.
"And another is looking to see if a criminal act has taken place and involved a third party.
"What does that all look like? You make sure you don't miss anything so rather than focussing on 'it is just an accident or just a criminal act or she went on her own volution' - you capture all the evidence."
The former Det Supt also said police would have combed that bench where Nicola's phone and her dog's harness were found.
She said: "Forensics on an outdoor scene is always really complex and usually confined to a small area.
"I am pretty sure they would have examined that bench or given consideration to that bench.
"They would look to see if there were any marks that could have assisted like drag marks or slip marks.
"They would be looking for any items such as her mobile phone and the dog harness - it is all relevant? And then they would look at the broader scene."
She also shared her thoughts on if she thinks there is enough evidence for it to be considered a criminal act.
She said: "You would have had to of taken her some distance to get her away from the scene.
"If something bad happened to her at the scene you'd think you'd find her close by.
"That is what would make it less likely to think it's a criminal act, there is not a lot of supporting evidence."
When the Mirror asked about the River Wyre and the ongoing search there she wasn't surprised police hadn't found anything yet.
The former Det Supt said: "It's also really difficult with rivers because they are tidal and with recent rainfall, it can be months before they reappear somewhere.
"I can only speak from my own experience from the Somerset coast, we saw people get washed across from Wales to Somerset and that can take some time for that to happen.
"The fact she hasn't been found yet, I wouldn't say that is unusual at this stage."
Nicola's disappearance has gripped the nation as seven days on it appears there are no leads into finding out what happened.
Since Nicola was reported missing, it appears there haven't been any major developments or further answers into what has happened.
Yesterday, search efforts ramped up as divers were seen going into the river.
Lancashire Police also appealed for a second potential key witness to come forward, who was later identified but said she hadn't seen Nicola that morning.
Nicola was last seen shortly after dropping her daughters off at school and taking her dog for a walk.
Ms Mackay said there will be a lot of work going on in the background that the public will not be aware of.
She said: "They will look at her social media footprint, what she has been interested in, going through her contacts, looking to see how she's behaved.
"There are a lot of things that happen around an investigation but we only see a really small search.
"I think you should bear in mind as the reader they won't be scratching the surface saying 'oh dear, she disappeared' they will be looking at every opportunity to see if there are any other clues and hypothesises.
"They will be looking at other crime factors as well."
She added: "It is more likely to be a misadventure than a criminal but that would not be ruled out at this stage.
"Until she is found the police will be working on this to help her family understand what's happened.
"It's horrible when someone goes missing like this and you don't understand where and why.
"Whatever the outcome now it's probably going to be tragic but that doesn't mean you give up."
Nicola is described as white, 5ft 3ins tall, with light brown shoulder-length hair. She speaks with an Essex accent.
She was last seen wearing a long black gilet jacket with a hood, black jeans and olive-green ankle wellies. Her hair was tied into a ponytail.
Anybody who has seen Nicola, or has information about where she might be, is asked to call 101, quoting log 565 of January 30th. For immediate sightings please call 999.
