Detectives are continuing the search for mother of three Gaynor Lord as her family mark a week since her disappearance.
Officers said there is a “high probability” that Ms Lord went into the River Wensum in Norwich, where a huge search is being conducted by specialist divers.
Police said they have not been able to establish her state of mind when she went missing with “any degree of confidence”.
It comes as a friend of Ms Lord said she was “upbeat and happy” and talking about Christmas just days before she disappeared.
Julie Butcher said her friend seemed “fine” when they last met on Tuesday last week.
“We were talking. She was a bit busy but we were talking about Christmas and she seemed fine, no different to the usual Gaynor. She was quite upbeat and happy,” Ms Butcher told the BBC.
Ms Butcher told the broadcaster she spoke to her friend at 2.15pm on Friday last week but she had to cut the call short to speak to a client.
“I said I would call her back and she said ‘yes’,” Ms Butcher said.
Ms Butcher said she returned the call but could not get through. She also sent a message to tell her friend she was free.
“I think she was still at work when she called me, I don’t know but maybe that’s why she couldn’t answer,” she said.
“I keep going over the conversation. If I hadn’t answered that call would she have talked to me? I feel terrible. I feel so sorry for the family.”
Ms Butcher said she received another call form Ms Lord at 4.15pm but it “sounded like a pocket call – I could hear movement in her pocket”.
Norfolk Constabulary released CCTV footage of what they believe is the last sighting of Ms Lord before she disappeared in Norwich on Friday December 8.
The 55-year-old disappeared after leaving work early in Norwich city centre at 2.45pm.
Her belongings were found in Wensum Park – around 1.5 miles from her workplace at Jarrolds department store – and her coat was discovered in the river that runs through the park.
Police said Ms Lord’s clothing, mobile phone, glasses and jewellery, including two rings, were discovered at various locations in the park.
The CCTV clip shows Ms Lord, wearing glasses and a long coat, walking along St Augustines Street in Norwich, which is busy with traffic, at 4.01pm on Friday.
Chief Superintendent Dave Buckley said it will take “a couple of days” or longer to complete the search of the stretch of river, which has included using sonar equipment.
“It’s very, very challenging – the river is very, very full of water with all the rain, full of lots of debris. The divers can see about one foot in front of them,” he said.
“So it’s an extraordinarily challenging environment for them to work in.”
Mr Buckley said the force was keeping an open mind about what happened to Ms Lord but “everything we know is pointing to a high probability that Gaynor went into the water”.
He said CCTV footage did not reveal anything about the motivations for Ms Lord’s actions.
“There’s nothing we’ve been able to establish that really gives us a clear position on her state of mind that I would feel any degree of confidence of saying what we think it is at the moment,” he said.
“We continue to talk to friends, family, anybody who can help us that we know she’s had contact with.”
Mr Buckley said officers had “some indications” of why Ms Lord left work more than hour before she was scheduled to finish.
But he added: “We’re just cautious of everything we know at the moment because clearly we’ve ended up in the situation we have, which is not usual.
“I don’t think any of the conversations we’ve had are completely informing us as to why her state of mind ended up being what it was.”
Mr Buckley said the force “can’t explain some of her behaviour that day”, adding: “We’re working really closely with family, with friends, with anybody else who might have had contact with her in the recent days or weeks to try and understand why this might have happened.”
He said officers are supporting her family, adding: “People are very shocked by what’s happened. Nobody knows why she’s done what she’s done.”
The Daily Telegraph reports Ms Lord told a colleague in the week before her disappearance that she “was feeling a bit funny, a bit off”.
The colleague, who did not want to be named, told the paper: “She said something about feeling a bit funny. It was very nonchalant. She said she was feeling a bit funny, a bit off.
“It was a brief conversation on either Thursday or Friday.
“She shook her hands as she said it but I didn’t think much of it.”
Police confirmed they have consulted officers from Lancashire Constabulary who worked on the search for Nicola Bulley.
Ms Bulley’s body was found in the River Wyre in Lancashire on February 19.
The Lancashire force was criticised over its handling of that investigation and the disclosure of Ms Bulley’s personal information.
