A former assistant nurse convicted of murdering a patient in 2003 is set to be exonerated after prosecutors on Monday did not contest new evidence presented by her defense team during the first hearing of her retrial.

Mika Nishiyama, 40, has spent 12 years in prison after being found guilty in 2005 of killing a 72-year-old man by removing his respirator at a hospital in Shiga Prefecture, western Japan.

But at the hearing at the Otsu District Court, the prosecutors did not contest new defense-submitted evidence including a doctor's opinion that the patient died of natural causes.

"We will put the matter in the hands of the court based on the evidence submitted during the previous trial, in which her conviction was finalized, as well as the retrial," a prosecutor said.

The prosecutors did not say whether they would support Nishiyama's acquittal.

(Mika Nishiyama, center, and her supporters head to the Otsu District Court on Feb. 3, 2020.)

"The defendant did not remove the patient's respirator and his death was natural. It is clear that her confession was a lie because its key points drastically changed," a defense lawyer said, urging the court to exonerate her.

The retrial will conclude next Monday, with a ruling expected to be delivered on March 31.

The former nursing assistant was indicted after admitting to killing the patient during police questioning in 2004, but she later retracted her confession, saying she had been coerced by interrogators.

She pleaded not guilty in subsequent court proceedings, but the Otsu court ruled her confession credible and gave her a 12-year jail term in 2005, which she finished serving in August 2017.

After Nishiyama sought a retrial, the Osaka High Court ruled in December 2017 that it was possible the patient died from natural causes based on new evidence submitted by the defense team, which included a doctor's opinion that pointed to arrhythmia as a possible cause of death.

A retrial was ordered after the high court refuted the credibility of Nishiyama's confession. The prosecutors appealed the decision but it was rejected by the Supreme Court in March last year.

In talks held with the court and defense lawyers in preparation for the retrial, the prosecutors initially said they planned to retain their guilty claim. But in October last year, they reversed their stance, saying they would not seek new evidence to prove their case.