A coronial inquest into the suspected death of missing Perth mother Robyn Santen has revealed her family and police believe she died after walking into the ocean.
A massive air, land and sea search was launched looking for Ms Santen after her unlocked car was found at City Beach car park with the keys still in the ignition on Sunday August 9, 2015.
The 36-year-old engineer and mother of two young children, aged three and five, was last seen getting dropped off by a taxi at her West Leederville home around 10:30pm the night before after having dinner and drinks with work colleagues in Northbridge.
The Coroner heard during opening statements Ms Santen and her husband Troy Santen had separated five weeks prior to her disappearance by her choice.
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Counsel assisting Coroner Barry King, Sergeant Lyle Housiaux, said Ms Santen was depressed about the breakdown of the marriage and the subsequent disagreements she and Mr Santen had been having about custody of the children, emailing her father and saying it was "getting nasty".
She had also previously suffered from post-natal depression and was receiving ongoing counselling for mental health issues.
After returning to her home following her work drinks, police believe Ms Santen found a letter left on her kitchen counter by Mr Santen outlining her mental health issues and their Family Court proceedings regarding custody of the children.
He was not living in the family home at the time.
The next day, as police launched a search for Ms Santen, the letter was handed to police by Mr Santen, after it was found screwed up on Ms Santen's floor.
The last known text message sent from Ms Santen's mobile was to Mr Santen just after midnight the night she disappeared, saying "Fuck you".
It was received via a Telstra tower in City Beach leading police to believe she likely sent it from City Beach rather than her West Leederville home.
The court heard an extensive six-day search uncovered no trace of Ms Santen or evidence of criminality.
Public appeals from distraught family members also failed to find Ms Santen.
Officer-in-charge of the police missing person's unit, Detective Sergeant Stephen Perejmibida, agreed while giving evidence that if Ms Santen entered the water on August 8, she either drowned while swimming in rough seas, committed suicide, or was taken by a shark.
"All avenues have been exhausted," he said.
"Though there is no direct evidence to confirm she is deceased... it is unlikely she is alive."
Her family are united in their belief she is deceased.
A survival expert contracted by WA Police to examine the case concluded if Ms Santen had entered the water, she would not have survived past August 10.
Ms Santen's mother in law, Gaye Santen, said during evidence, she wished her daughter-in-law, who was described during proceedings as a "kind and generous person", had opened up more to her about her mental health issues.
"Maybe mental health is such a stigma that she didn't want to advertise it," she said.
"She never asked me for help, I wish she had."
Mr Santen gave evidence that his wife had talked about suicide several times, and that he had been supportive in helping her to seek treatment and counselling.
He said he "felt bad" about the letter he left her the night she disappeared for a long time as he believed it was "clearly a catalyst" for her suspected death.
The inquest continues.
For anyone seeking crisis support or needing help, contact Lifeline: 13 11 14 or lifeline.org.au