Alleged killer neonatal nurse Lucy Letby was repeatedly told she was not permitted to enter a room where parents were grieving their baby she allegedly murdered. 

Letby, 32, is standing trial in the U.K. for allegedly murdering seven babies and attempting to murder 10 more at the Countess of Chester Hospital’s neonatal unit between 2015 and 2016.

The prosecutor said she injected some infants with insulin or milk, while others she injected with air. She allegedly attempted to kill one baby three times.

The jury heard testimony from a senior nurse who was working with Letby at the hospital's neonatal unit at the time the babies died, according to the BBC.

COLLEAGUE OF ALLEGED KILLER NEONATAL NURSE THOUGHT ‘NOT AGAIN’ WHEN NEWBORN GIRL COLLAPSED DAY AFTER TWIN DIED

Neonatal nurse Lucy Letby

Neonatal nurse Lucy Letby, 32, is alleged to have murdered seven babies and attempted to kill 10 more. (SWNS)

The senior nurse, whose identity was not released publicly per court order, was shift leader the night one of the babies, designated "Child C," collapsed and eventually died.

Letby was not Child C's designated nurse the night the child died, but the senior nurse said Letby had to be told more than once to stop going into the room where the parents were grieving after resuscitation attempts on their child were stopped.

Letby was told instead to leave the family to the deceased baby's designated nurse to focus her attention on a different baby who was not doing well, the witness told the court.

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Police search Lucy Letby home

Cheshire Police in the U.K. search the home of Lucy Letby in 2018, when they found handwritten notes that were shown to jurors this week. (Peter Byrne/PA Images via Getty Images)

The senior nurse also said upon cross-examination that the hospital's neonatal unit was facing increased demand despite static staffing levels, but maintained that the quality of care provided to Child C was not diminished by that.

Letby was a "constant, malevolent presence" in the neonatal unit of the hospital in northwestern England, prosecutor Nick Johnson argued before a jury when Letby's trial opened in September.

ALLEGED KILLER UK NEONATAL NURSE TRIAL: TWINS' MOTHER PLEADED FOR CHILD'S LIFE: ‘DON’T LET MY BABY DIE'

The Countess of Chester Hospital

The Countess of Chester Hospital, where nurse Lucy Letby used to work in Chester, England. (Christopher Furlong)

Johnson told jurors "a poisoner was at work" at the hospital, which he said had been marked by a "significant rise in the number of babies who were dying and in the number of serious catastrophic collapses" after January 2015, before which he said its rates of infant mortality were comparable to other busy hospitals.

Investigators found Letby was the "common denominator," and that the infant deaths aligned with her shifting work hours.

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Letby pleaded not guilty to seven counts of murder and 10 counts of attempted murder. Her trial is slated to last up to six months.