A retired detective said Nicola Bulley may never be found if she has drowned in the River Wyre, as police fear.
Former detective superintendent Howard Millington said third-party involvement was highly unlikely, but admitted the case was "very bizarre", though is "probably going to end in a tragic outcome".
Lancashire Police yesterday announced the search had been extended up to the sea after scouring the river has so far proved fruitless.
Superintendent Sally Riley said detectives ruled out any foul play, but admitted no significant evidence has been found.
The 45-year-old vanished on a dog walk in St Michaels on Wyre on January 27, with her phone found on a bench overlooking the water.
A major search effort has been launched, which includes drafting in independent underwater forensic experts Specialist Group International this week.
Mr Millington said the police would have moved quickly during the case’s ‘golden hour’ to exhaust the majority of hypotheses - and if she was potentially snatched or attacked investigators would have said by now.
He told the Mirror: “Witnesses haven’t heard any screams or seen any disturbance.
“No clothing has been found, along with the open nature of the area and the fact that it’s popular with dog walkers and this was nine o’clock in the morning, it’s light...
"All those things taken together lead to the most likely hypothesis being that she’s slipped and fell for whatever reason into the water.”
Referring to complaints that the bench where Nicola’s phone was found wasn’t cordoned off initially, he said this would only need to be done if there was cause to believe a criminal act had taken place.
“They’ll have done a meticulous search, there’s science behind it, it’s not just random,” Mr Millington - who worked for Greater Manchester Police for 30 years - explained.
“If it was treated as a missing person inquiry, there’s no suggestion of foul play. You would be more focused on searching for the person than preserving evidence of a crime that probably hasn’t happened,” he continued.
He said if a third party was involved then there would be specific tell-tale signs - including blood staining or reports of suspicious people in the area by now.
“I am almost certain there has been nothing flagged up to the police,” he said.
“Most people, if she had been murdered or abducted, most people in this country, it’s by somebody that’s known to them.”
Mr Millington said her family and friends would have been quickly spoken to and alibis confirmed to rule them out.
“If there was something worrying them, [police] would have gathered a vast amount of information so far.
“Then they would be saying they are keeping an open mind and including that it could be suspicious and they are not saying that.”
He added: “There’s no way they would be misleading the public, especially if there was a real concern around community safety.”
However, he said if significant new evidence suddenly came forward, then investigators would be able to change tact.
Asked how long the police would keep searching for a body, he said: “They can’t search forever.
"There’s not a lot else they can do.
“If she’s ended up in the estuary or the sea, it could take a while. It could even be never. I hope it isn’t but it’s possible.”
