Children's author Helen Bailey could have been put in a martial arts neck lock while drugged and then suffocated, a court has heard.
The body of the successful 51-year-old writer was found alongside her beloved dachshund Boris submerged in "human excrement" deep below her lavish property in Royston, Hertfordshire, in July 2016, a jury at St Albans Crown Court was told.
Her fiance, Ian Stewart, 56, of Baldock Road, Royston, is accused of drugging and killing her, before dumping her body in a cesspit at the home they shared.
Home Office pathologist Dr Nat Cary told the court that Ms Bailey could have been killed by a "subtle" method of suffocation - or even still been alive when she was put in the septic tank.
The defendant denies charges of murder, preventing a lawful burial, fraud and three counts of perverting the cause of justice.
Dr Cary said although there were no "obvious" signs of physical injury, the sedative Zopiclone was found in Ms Bailey's system.
The sleep drug was prescribed to Stewart and toxicologist Dr Mark Piper said hair analysis of the victim suggested it was "ingested on more than one occasion".
Although the cause of death was "undetermined", Dr Cary said if Ms Bailey was in a sedated state she could have been killed without necessarily displaying signs of harm.
He said: "Even the most meek and mild person would not put up with being smothered when they are awake."
He said: "Subtle modes of death include smothering and compression of the neck by means including an arm lock, using the crook of the elbow ... also called a sleeper hold, it is used in certain martial arts to reduce consciousness.
"That is another possibility to consider."
But on cross-examination by defence counsel Simon Russell Flint QC, he said this was only speculation.
He also agreed it was possible that the author could have still been alive, albeit sedated, when she was put in the septic tank.
He said: "I am not (sure) but, on the basis of the case as a whole, it is my opinion that not only was she concealed by a third party but it seems likely she died at the hands of the third party by some means."
He added: "In my view it's unlikely that natural diseases played any part here. Natural disease won't cause you to end up in a cesspit."
Jurors were told it was possible that Ms Bailey had consumed the sleep drug unknowingly, perhaps with food or drink, but Dr Cary later said he could not know for sure.
It is alleged that the killing had "money as its driving motive", with Stewart in line to be a "substantial" benefactor of the author's £4 million fortune in the event of her death.
Ms Bailey had been missing for three months when police officers opened the hatch to the cesspit beneath her garage and saw an arm protruding from the waste.
The court heard that she was fully clothed, except for her bare feet.
Stewart's GP, Dr Afshan Khan, said she had prescribed the sedative to him on January 25 - describing the drug as "very mild".
On Tuesday, the court heard that Ms Bailey had become concerned about feeling unnaturally sleepy in the weeks leading up to her death.
She used a search engine to look up terms including "can't stop falling asleep" and told her family she felt forgetful.
But when asked if she had heard about the drug making patients fall asleep suddenly, Dr Khan said she had not.
She added that Zopiclone could only be considered a safe drug when used by a patient to whom it was prescribed.
Jurors were told by Dr Piper that traces of it were found in Ms Bailey's hair, chest cavity fluid, liver and thigh muscle.
Due to the amount of time that had passed between her alleged time of death in April and the discovery of her body in July, he said it was difficult to say how much was in her system when she was killed.
Samples of her hair were split into four sections for analysis, with each said to represent a four-week period, with the most recent closest to the scalp - representing a "historical profile".
Zopiclone was found in all four, but in such small doses in the farthest away from the scalp that it was said it could have been contaminated.
Dr Piper told the court that in the hair sample closest to the scalp it was of a "significant" concentration.
He said: "It is above the level that scientists recognise as a single, one-off event."
The court heard that among the side-effects of Zopiclone was short-term memory loss.
Dr Piper agreed, when asked by the prosecutor, that this could lead someone to have concerns about their "state of mind".
The drug was also said to create a metallic, bitter taste in the mouth when consumed - caused not by the tablet itself, but a subsequent chemical reaction when it takes effect.
A post-mortem examination of Boris the dog was unable to determine the cause of his death, the jury was told.
A statement from veterinary surgeon Dr Jonathan Williams said decomposition of the remains meant it was not possible to "confirm or refute whether the animal drowned".
He added that there was "no evidence of skeletal trauma" in the pet.
The trial continues.