Neonatal nurse Lucy Letby allegedly murdered a baby weighing less than two pounds by forcing air into his stomach, a jury was told this week.

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 prosecution said Letby caused the premature newborn’s sudden collapse and death during the night shift of June 13, 2015, by injecting a fatal amount of air into his stomach via a nasogastric tube (NGT), according to the BBC.

Expert witness Dr. Dewi Evans told the jury that he believes the alleged victim, also known as „Child C,“ died from a „splinting of the diaphragm.“ He said there were „three scenarios“ by which air could be used to kill an infant: air through the NGT, air traveling intravenously or a combination of both.

LUCY LETBY REPEATEDLY TOLD TO STAY AWAY FROM GRIEVING PARENTS OF BABY SHE ALLEGEDLY KILLED: WITNESS

U.K. neonatal nurse Lucy Letby and a stock image of newborn babies

U.K. neonatal nurse Lucy Letby and a stock image of newborn babies (ER Productions Limited via Getty Images/SWNS)

In a cross-examination that at times became contentious, Letby’s attorney Ben Myers suggested Evans was „reaching“ to support the allegations against his client.

„If you really thought that splinting the diaphragm was a cause of death you would have stated that before today, wouldn’t you?“ Myers asked.

„In virtually all of the cases, I have benefited from additional information since then,“ Evans replied.

The maternity ward of the Countess of Chester Hospital in the U.K., where Letby worked and is alleged to have killed seven babies between 2015 and 2016.

The maternity ward of the Countess of Chester Hospital in the U.K., where Letby worked and is alleged to have killed seven babies between 2015 and 2016. (Christopher Furlong/Getty Images)

Evans also pushed back against Myers‘ claim that he was introducing new evidence „with the purpose of supporting the allegation rather than explaining the facts.“

„That is incorrect,“ Evans said. „I’m trying to explain what led to a baby, who was very small, suddenly collapsing and where resuscitation was unsuccessful.“

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

A police officer stands outside Lucy Letby's house in Chester on July 4, 2018, in Chester, United Kingdom.

A police officer stands outside Lucy Letby’s house in Chester on July 4, 2018, in Chester, United Kingdom. (Christopher Furlong/Getty Images)

„I’m not relying on my opinion alone, I’m relying on other people’s opinions as well. That is what doctors do, that is what we do.“

Evans later said it was „insulting“ that Myers would suggest he was not an independent witness.

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.

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.

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)

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.

Jon Brown is a writer for Fox News Digital. Story tips can be sent to [email protected]