A woman who smothered her toddler while suffering from severe depression and psychosis has been found not guilty of murder by reason of insanity.

The woman, who cannot be named by order of the court, had been on trial at the Central Criminal Court since yesterday charged with the murder of her young child at the family home last year.

The prosecution and defence told the jury she was suffering from a mental disorder at the time.

The jury deliberated for 54 minutes before returning with a unanimous verdict.

The woman was previously treated at the Central Mental Hospital for more than a year before being released on bail in advance of her trial. The court has directed she be committed again for treatment to the CMH.

The woman was hugged by family after the verdict was delivered and was comforted by her partner who was in court throughout the trial.

The jury heard she had suffered from a fixed false belief that her child had a severe form of autism and had no future.

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Two consultant psychiatrists told the jury the woman was suffering from a severe depressive epidsode with psychotic features when she smothered her child with a pillow as she took an afternoon nap on the couch.

Earlier Ms Justice Carmel Stewart had told the jury that to return a verdict other than one of not guilty by reason of insanity would "fly in the face of the evidence".

The court has previously heard that the woman became "obsessed" and "overwhelmed" with her child's autism diagnosis and convinced herself that the toddler had a more severe form of autism - Pathological Demand Avoidance (PDA) - when the reality was that the diagnosis was one of mild autism.

Ms Justice Carmel Stewart told the jury while the trial had been brief it was no less difficult for its brevity.

The judge said there was no dispute between the psychiatrists as to whether she was suffering from a mental disorder.

Technically you could return a guilty verdict but that would be "flying in the face of the evidence before you", she said.

In closing arguments, counsel for the prosecution told the jury the evidence in the case led "clearly and unequivocally" towards the special verdict of not guilty by reason of insanity.

Senior Counsel Paul Murray said the case starts with a mother suffocating her child, her first born and anyone looking at that would ask how could a mother in their right mind do that.

Prosecution case 'model of impartiality'

He said the jury could add to that the background evidence including her history of mental health problems since her college days, her obsession with her child's autism diagnosis and her fear of what the future held for that child and her family as a whole.

He reminded the jury of the evidence of both consultant forensic psychiatrists who concluded she had been suffering from a mental disorder at the time.

Counsel for the defence commended the prosecution for the case which he described as a "model of impartiality".

Senior Counsel Patrick Gageby told the jury that even leaving aside the evidence of both psychiatrists there was not adverse history and no evidence that the woman ever did anything wrong to anyone. If such a history had existed, it would have tumbled out, he said.

He said all the sign posts were there, the telling points for depression.

His client had a "fixed, false idea that her child was catastrophically suffering from the worst possible end of the autism spectrum disorder despite the fact that everyone told her that was not true".

Mr Gageby said the history was a telling feature of the case and that the "illness was in the driving seat".

A completely irrational belief was in the driving seat, he said. He said the woman believed the best way to achieve happiness for her family was to kill her child and that solution was not one which would lead anyone to consider a person sane.

He said two days after she was remanded in custody she was transferred to the Central Mental Hospital and immediately diagnosed and given not just anti-depressant but also anti-psychotic medication.

He said she had recovered substantially under the care of the CMH and that being so the evidence "goes all one way".

Earlier, a second consultant forensic psychiatrist told the court the woman was suffering from severe depression with psychotic features and fulfils the criteria for a special verdict of not guilty by reason of insanity.

Dr Stephen Monks, a consultant forensic psychiatrist, from the CMH gave evidence for the defence on the mental state of the accused.

Dr Monks agreed with Mr Gageby that the woman was a dedicated and caring mother but her mood began to dip around the summer of 2017.

The woman became increasingly preoccupied and ruminated about her child's health and the intensity heightened in the weeks leading to her child's death.

On the day of the killing, her behaviour was profoundly influenced by her depressive state and she was consumed by a feeling of hopelessness and despair. She was unable to generate coping responses and saw killing her child as the only solution, he said.

In summary, Dr Monks said the woman was suffering from a mental disorder, severe depression with psychotic features and did not know the nature and quality of the act as she believed her only option was to kill her child, who she was convinced was profoundly disabled and had no future or quality of life.

She fulfils the criteria for the special verdict of not guilty by reason of insanity, he said.

Yesterday a consultant forensic psychiatrist for the prosecution gave evidence that the defendant was suffering with "recurrent depressive disorder", which is a mental disorder and fulfilled the criteria for a special verdict of not guilty by reason of insanity.

Dr Sally Linehan from the CMH outlined that the accused did not know what she was doing was wrong and was unable to refrain from committing the act.

She was satisfied that the mother fulfils the criteria of not guilty by reason of insanity.