A judge overturned the conviction of a 64-year-old US woman, Sandra Hemme who has spent 43 years in prison after incriminating herself in a 1980 killing while she was a psychiatric patient.

According to Fox News, it was reported that the judge and the woman’s lawyers suggested a former police officer may have been the killer.

Judge Ryan Horsman ruled late Friday that the woman established evidence of actual innocence and must be released within 30 days unless prosecutors retry her.

The judge said Ms Hemme’s trial counsel was ineffective and prosecutors did not reveal evidence that would have helped her defence.

The attorneys of Ms Hemme who filed a motion seeking her immediate release, said this is the longest time a woman has been incarcerated for a wrongful conviction.

“We are grateful to the Court for acknowledging the grave injustice Ms Hemme has endured for more than four decades,” her attorneys said in a statement, pledging to continue in their efforts to dismiss the charges and allow Ms Hemme to be reunited with her family.

Ms Hemme was shackled in wrist restraints and so heavily sedated to the point that she “could not hold her head up straight” or “articulate anything beyond monosyllabic responses” when she was initially questioned about Jeschke’s death, according to her lawyers.

The lawyers said in a petition seeking Ms Hemme’s exoneration that authorities ignored her “wildly contradictory” statements and suppressed evidence implicating then-police officer Michael Holman, who attempted to use Ms Jeschke’s credit card.

The judge wrote that “no evidence whatsoever outside of Ms Hemme’s unreliable statements connects her to the crime”.