Italy killer nurse
Italian police conduct a search at Piombino hospitalCarabinieri Police

Judges in Italy have ordered the release from jail of a nurse suspected of killing more than a dozen patients at a public hospital. Fausta Bonino was arrested in the port city of Piombino at the end of March on suspicion that she injected lethal doses of an unprescribed drug to 13 people over a two-year period ending in September 2015.

Less than a month later, a Florence court ruled against the extension of her precautionary detention pending further investigation. The 56-year-old, who claims to be innocent, was allowed to leave her Pisa cell and return home on 20 April.

"It has been a nightmare," she was quoted as saying by local media. "Now someone will have to pay for the wrong done to me and my family. When this is over, I will denounce those who accused me unjustly."

Detectives alleged Bonino was responsible for the deaths of 13 men and women aged aged between 61 and 88 who passed away while they were receiving treatment at the anaesthesia and reanimation department of a state-run hospital in Piombino, where Bonino worked.

Many victims were said to have died of unexpected complications after arriving at the department in serious but not critical conditions. According to prosecutors, they were killed by the nurse with injections of high doses of heparin, an injectable blood thinner that caused internal bleeding.

Motives were not immediately clear and investigators suggested the anti-epileptic drugs taken by the accused might have affected her behaviour. Bonino and her family dismissed the allegation, saying she did suffer from the disease but the drugs she took gave her no side effects and she was an "absolutely normal woman," Il Corriere della Sera reported.

Judges in Florence didn't immediately explain the reasons behind their decision to release Bonino. Under Italian law, those accused of a crime can be detained ahead of trial only if they are at risk offending again, fleeing or corrupting evidence.

The verdict implied one or more of those prerequisites failed to hold. Italian media pointed to faulty evidence, including wire-tapping wrongly attributed to the nurse. Bonino's lawyer Renato Di Biagio said that if there was a murderer he/she was still free. His client remains under investigation.

The case came just weeks after another nurse was sentenced to life in jail for killing an elderly patient at a separate Italian hospital in Lugo, near Ravenna. Daniela Poggiali, who is also facing trial over the suspicious deaths of dozens more patients in her care, became infamous as the "killer nurse" after photos of her posing with her thumbs up near one of the victims were released.