German police and prosecutors are questioning a nurse accused of poisoning five premature babies with morphine at a hospital.

Five premature babies at the University Hospital of Ulm in southern Germany between the ages of one day and one month suddenly began experiencing life-threatening breathing difficulties on the morning of December 20 last year, authorities said in a statement.

The suspect was on duty at the hospital that morning and is was taken into custody on Wednesday. The nurse is being investigated for five counts of attempted manslaughter and grievous bodily harm. All the babies survived and police said they were not expecting any further health problems.

Police searched staff members’ lockers at the hospital and authorities confirmed Thursday at a press conference that they found a syringe containing breast milk among the nurse's possessions. Police and the public prosecutor also confirmed that forensic testing showed the syringe had been laced with morphine.

Christof Lehr, the Ulm's chief public prosecutor, said Thursday that the nurse denies having given the babies morphine. It was not immediately clear whether morphine may have been part of the babies’ treatment plan.

“In the early morning hours of December 20, 2019, five premature babies housed in a room in the Clinic for Pediatric and Adolescent Medicine in Ulm almost simultaneously suffered from life-threatening breathing problems, which, fortunately, thanks to the immediate intervention of the hospital staff, remained without consequences according to current medical assessments,” investigating authorities said in a statement.

The hospital alerted local police after morphine residue was found in the babies’ urine samples.