ROME, Italy (AFP) — An Italian nurse has been arrested on suspicion of being a serial killer who administered fatal doses of a blood-thinning drug to 13 intensive care patients in less than two years.

Fausta Bonino, 56, allegedly killed the patients aged between 61 and 88 between January 2014 and September 2015 at a hospital in the Tuscan town of Piombino, local police told a press conference yesterday.

Investigators believe that the victims, all seriously but not terminally ill, died as a result of being given strong doses of the anticoagulant drug Eparina.

“None of the victims’ lives had been in danger at the time the drugs were administered,” said Erasmo Fontana, one of the detectives involved in the investigation.

Marketed as Heparin in the United States and other markets, the drug is used to prevent blood clotting.

Bonino is accused of having given her victims up to 10 times the usual dose of the drug, including in certain cases where it had not been prescribed by the physicians treating the patients.

The result, police said, was to rapidly trigger multiple and irreversible internal bleeds which killed 12 of the alleged victims. The other one died from cardiac arrest.

Bonino was arrested Wednesday after a review of all the recent abnormal deaths at the hospital identified her as being the only staff member involved in every case.

The review was triggered after the unit’s death rate for admitted patients spiked from 12 per cent to 20 per cent.

Police at yesterday’s press conference said the arrest had potentially averted further deaths.

But local newspaper Il Tirreno suggested the hospital authorities may have had suspicions about Bonino early last year. The nurse was moved from the intensive care unit in October 2015 to a role in which she had no contact with patients, according to the paper.

“In the horror rankings we have reached a new peak of human misery,” Health Minister Beatrice Lorenzin said in a statement on what may prove to be one of the biggest serial killings in Italy’s history.

Bonino has been imprisoned pending formal charges. Prosecutors want her to be charged with multiple homicide with a number of aggravating factors, including cruelty and neglect of her duties as a nurse and public servant.

Police said that the married mother of two grown-up children had been treated for depression and Il Tirreno reported she also had problems with alcohol and prescription drugs.

Bonino’s case follows that of Daniela Poggiali, a 44-year-old former nurse who received a life sentence in early March for the murder of one of the 38 patients she was initially suspected of having killed at a hospital in southern Italy.