The second day of the trial of alleged killer nurse Lucy Letby has begun today (Picture: SWNS / Facebook)

An alleged killer nurse ‘refined’ her murder method before killing a five-year-old baby by injecting air into his stomach, a court has heard.

Lucy Letby, 32, is accused of a year-long spree targeting premature and sick newborns at the Countess of Chester Hospital in Cheshire between 2015 and 2016.

Letby allegedly killed the baby boy, child C, just six days after murdering for the first time, when she killed another baby boy, child A.

Just days later she is accused of attacking his twin sister, child B, while working at the neo-natal unit at the Countess of Chester Hospital.

Child C died because the air injected into his stomach made him unable to breath and he suffered a cardiac arrest, the court heard.

Nick Johnson KC, told the jury on the second day of the prosecution at Manchester Crown Court.

The boy had been born prematurely at 30 weeks on June 10, 2015, weighing only 800 grams, but despite going into intensive care was in good condition.

Five days later, on the night shift of June 14, Letby was supposed to be looking after another, more poorly baby, in another room.

But she was the only person in the room when Child C suddenly and unexpectedly collapsed.

Letby, 32, denies seven counts of murder and 10 counts of attempted murder.

Nurse Lucy Letby appeared in court today (Picture: SWNS)

The alleged killer is said to have injected air into babies (Credits: REX/Shutterstock)

She appeared in court today (Picture: PA)

She is said to have poisoned two of her victims with dangerous doses of insulin days after they were born.

The methods allegedly used in other cases are expected to be detailed later in the trial.

Concerns were first raised when the number of deaths at the hospital’s ‘closely restricted’ neonatal ward suddenly doubled in a year.

A criminal investigation was launched after a slew of independent investigations failed to find an explanation.

Doctors eventually ‘noticed that the inexplicable collapses and deaths did have one common denominator’, prosecutors told the court: ‘The presence of one of the neo-natal nurses.

‘And that nurse was Lucy Letby.’

More: News

The 32-year-old, from Hereford, denies seven charges of murder and 15 of attempted murder.

The 17 alleged victims, who cannot be named in the media for legal reasons, will be referred to as Babies A to Q.

Opening the prosecution case yesterday, Nick Johnson KC said consultants began raising concerns after a number of babies died after ‘deteriorating unexpectedly’.

He continued: ‘Not only that, when babies seriously collapsed they did not respond to appropriate and timely resuscitation.

‘Some of the babies who did not die collapsed dramatically but then – equally dramatically – recovered.

‘Their collapse and recovery defied the normal experience of treating doctors.’

He continued: ‘Babies who had not been unstable at all suddenly deteriorated. Sometimes a baby who had been sick but then been on the mend suddenly deteriorated for no apparent reason.’

The trial continues.

This is a breaking news story, more to follow soon… Check back shortly for further updates.

Got a story? Get in touch with our news team by emailing us at [email protected]. Or you can submit your videos and pictures here.

For more stories like this, check our news page.

Follow Metro.co.uk on Twitter and Facebook for the latest news updates. You can now also get Metro.co.uk articles sent straight to your device. Sign up for our daily push alerts here.

The alleged killer nurse is said to have ‘refined’ her techniques as she is said to have killed more babies.