Nicola Bulley’s Fitbit explains exactly what time she entered the river

Her body was found in the River Wyre three weeks later on February 19, after which a post-mortem gave her cause of death as drowning.

A two-day inquest into the 45-year-old’s death got underway yesterday at Preston’s County Hall with statements from police, pathologists and two witnesses who reported hearing a scream.

Witness Veronica Claesen told the hearing: "I was just about to get into the car and I heard a scream.

“A very short scream and my immediate thought was, ‘Somebody is having a bit of fun at the back of the graveyard’.”

A second woman, Helen O'Neill, said she had been in the garden with her dogs not far from the location where Bulley disappeared.

She said: "I heard a scream, it's not an alarming noise, it was just over in a couple of seconds. I'm quite used to hearing the children in the school out back, but it was not that noise.

"I vividly remember thinking it's unusual at this time. In my head, I had two females, walking along by the river and one jumped out on the other. I didn't think anything of it until later on.”

Based on analysis of Bulley’s Fitbit and iPhone, DC Keith Greenhalgh believes that the mum of two “very possibly” entered the water at 9:22am, as her Fitbit stopped working at 9:30am.

PC Matthew Thackray from the North West Police Underwater Search & Marine Unit described the likely entrance point into the water as a “cliff edge” from which “there is nothing to grab hold of to help yourself back out."

The officer noted: "It's my belief that if she did fall in she was probably floating and being pushed along the flow."

The inquest heard that the water was a bracing 4C on the day of the disappearance, which medical experts say is cold enough to cause cold water shock.

Diving expert Professor Mike Tipton imagines that Bulley would have lost consciousness almost instantly after taking in “one or two breaths” of water.

Professor Tipton said: "The lethal dose of water into the lungs, with freshwater, is two litres.

"In that first breath, you would have taken in 1-2 litres. So it would only take maybe one or two breaths to cross the lethal dose."

Cold water expert, Dr Patrick Morgan, concurs with the professor, adding the “heart pumps no blood and the brain switches off.”

Dr Morgan said: "On the occasion that the individual has taken that initial gasp on the surface of the water and then gone below, the duration would be 10 seconds that you could hold your breath and very likely one or two seconds at best."

Home Office pathologist Dr Alison Armour, who carried out the post mortem on Bulley, gave her cause of death as drowning.

Dr Armour told the inquest: “I gave the cause of death as drowning.

"The watery fluid identified within the stomach and also in the lungs themselves are classical features as we see in cases of drowning.”

She added: “Ms Bulley was alive when she entered the water - because it is an active process to swallow and inhale water into lungs.

"My opinion as to the cause of death is that it was drowning.”

The pathologist also said Bulley had not been drinking before her death.

Lancashire Police previously revealed the mother-of-two had struggled with alcohol and perimenopause.

The force faced criticism for disclosing such private information but the Information Commissioner's Office last month announced it would not take any enforcement action over the remark.