Early summer 2015 and a young mum-to-be was admitted to the Countess of Chester Hospital.

She had nine weeks to go before her due date, but doctors were so worried by her high blood pressure, they decided to deliver her twins immediately by Caesarean section.

The operation went smoothly enough, the boy weighing in at 3 lb 12 oz and his sister a fraction lighter. The girl was born blue and floppy and with a low heart rate, and was placed on a ventilator. Her brother breathed on his own and was more stable. Both were immediately moved to the hospital’s neonatal unit, where they were placed side by side in incubators in Nursery One — reserved for the sickest of the new arrivals.

‘Sometimes the smallest things take up the most room in your heart,’ read a poster pinned to the wall in the corridor outside. It was something the mother and father of the babies, who for legal reasons we shall call Baby A and Baby B, already knew.

They had dreamed of starting a family for years and now all they could do was hope for the best. Because it is hope that drives much of what goes on in a neonatal unit. Hope that babies born prematurely or born unwell will survive those vital first few hours. Hope that as the days pass, heart rates steady, tiny lungs strengthen and weight is put on.

And hope that the doctors and nurses in whose hands the lives of their loved ones rest will do their very best for them.

The hospital’s neonatal unit was not untypical of those found in general hospitals up and down the country. At its core were the four treatment rooms where up to 16 babies could be cared for at any one time.

Nursery One, known to nurses as The Hot Room, was the intensive-care unit, with one nurse assigned to each baby. Next door was the high-dependency unit, Nursery Two, where a nurse might be designated two babies to look after in their shift.

Nursery Three and Nursery Four were used as ‘growing’ rooms for babies who needed to establish a good feeding regime before they could be discharged.

As for the medical staff, at the top of the pyramid were the consultants, followed by the registrars and then the senior house officers.

The nursing staff totalled about 25 nurses and 15 nursery nurses.

They worked either day or night shifts or a combination of the two. The day shift started at 7.30am; nights at 7.30pm. Parents would visit during the day, meaning that at night there were significantly fewer people around.

As for who cared for which baby, that was down to the shift leader, designating nurses to each tiny patient.

And so it was that on June 8, 2015, as the day shift handed over to the night shift, a new nurse was designated to Baby A. The nurse’s name was Lucy Letby. When she came on to the ward Baby A — the boy — was assessed as ‘doing well’. Within an hour and a half, he was dead.

Babies A and B: ‘You need to let him go’

Date of attacks: June 8 and 10, 2015

VERDICT: Guilty of murdering Baby A and attempting to murder Baby B

The first sign that anything was wrong came at 8.20pm when Baby A — the boy and the stronger twin at birth — suddenly stopped breathing. Letby was the only nurse to witness his collapse, which occurred around the time she set up a drip to give him a glucose infusion.

She called a doctor and staff frantically attempted to resuscitate the child. Baby A’s parents, watching television in a side room, rushed in.

‘Please don’t let my baby die, please don’t let my baby die,’ Baby A’s mother begged, sobbing uncontrollably.

But after the baby failed to respond, the child’s grandmother told her daughter: ‘You need to let him go.’

Heartbroken, she agreed, nodding to the medics to stop chest compressions.

As his family were comforted in a side room, Letby took Baby A’s hand and footprints, as well as a lock of his hair.

The nurse, whose name badge was adorned with the image of a butterfly, said she thought it was a ‘nice thing to do’.

Meanwhile, medics, some tearful, struggled to understand what had happened. An immediate post-mortem examination failed to provide any answers. But what did strike them as unusual was a rash they had seen on the boy’s skin — patches of pink and blue that came and went.

They did not know it then, but that flitting rash would become a ‘hallmark’ of a number of the deaths.

The cause? Air that Letby had injected into the bloodstream of her victims, it was claimed. In the case of Baby A, it had probably been administered through his drip. But Letby gave the impression that she was as devastated as her colleagues.

Like most 25-year-olds, she was a regular phone and social media user. And in the hours after Baby A’s death she searched Facebook multiple times for the name of his mother, and sent WhatsApp messages to a colleague saying she hoped her shift the following night would be ‘more positive’.

Naturally, after Baby A’s death his parents became desperately worried about the wellbeing of his sister Baby B. They spent the day cuddling her, and only in the evening were they persuaded to go for a rest.

‘The next thing I know we were getting woken up by a nurse,’ the mother would tell the court.

‘My heart sank,’ she said. ‘Not my baby. Not again.’ This time, Letby was not caring for their daughter. But in the early hours of June 10, she did help the designated nurse start a bag of intravenous feed.

At about 12.30am — 27 hours after Baby A had collapsed — an alarm monitoring Baby B activated and Letby called for help.

Baby B looked like her brother had done the night before — she was grey and her skin showed the same blotched, purple discolouration.

With the infant’s heart rate dropping, Letby and other medics started to resuscitate her. Thankfully, this time the baby recovered, and a month later would be allowed home, suffering no apparent after-effects.

But an expert paediatrician who subsequently reviewed the incident concluded that Letby had in some way ‘sabotaged’ Baby B and may also have injected her with a dose of air.

Baby C: ‘Call the priest’

Date of attack: June 13, 2015

VERDICT: Guilty of murder

Ahead of her shift shortly after the death of Baby A and the emergency with Baby B, Letby told a colleague she wanted to go straight back to looking after babies in intensive care. She found the other nurseries ‘boring’ and ‘didn’t just want to feed babies’. But arriving for work on the evening of June 13, she was placed in Nursery Three.

Baby C, who weighed less than a bag of sugar when he was born ten weeks early, was in Nursery One. Although tiny, he was doing well.

At 11.15pm, having given him his first feed of milk, his nurse, Sophie Ellis, nipped out of the nursery for a few moments, only to hear an alarm monitoring breathing and heart rate going off. When she returned, Letby was there, standing over Baby C’s incubator.

The child recovered quickly and Nurse Ellis sat down at a computer in the nursery, with her back to the cot. But 15 minutes later he collapsed again.

When she turned to attend, Letby was again by his cot. This time a crash call was put out.

As the medics struggled to get the boy breathing, his mother, herself a GP, was summoned from the ward where she was recovering from a Caesarean section.

‘I didn’t take in the severity of the situation until a nurse came up and asked whether I wanted someone to call a priest,’ she told the court. ‘I remember feeling quite shocked and I asked if she thought he was going to die. She responded: “Yes, I think so.” ‘

Soon after midnight it became clear the boy could not be saved. Dr Katherine Davis, a paediatric registrar, told jurors she was surprised by Baby C’s lack of response to resuscitation attempts. ‘Even the smallest, sickest babies will usually respond in some way,’ she said.

‘We get them back for a short period . . . this was very unusual that he had absolutely no response.’

The boy was kept alive until he had been baptised, dying at 5.58am on June 14. His father later told police that a nurse he thought may have been Letby came in before that with a ventilated basket and said: ‘You have said your goodbyes — do you want me to put him in here?’

The father said he found the comment shocking because their baby was still alive.

Dr Dewi Evans, the prosecution’s expert witness, concluded the boy died because air had been injected not into the bloodstream, as before, but directly into his stomach via a feeding tube.

This would have prevented the diaphragm from moving up and down and filling the lungs with air, suffocating the child.

Again, Letby searched for the child’s parents on Facebook and messaged colleagues. ‘No one should have to see and do the things we do,’ she wrote. ‘It’s heartbreaking, but it’s not about me. We learn to deal with it.’

Baby D: ‘There’s a Reason For Everything’

Date of attack: June 22, 2015

VERDICT: Guilty of murder

Baby D was one of the few babies in the neonatal unit who was not premature. She weighed 6 lb 14 oz when born by C-section, but she needed oxygen soon after birth and so was admitted.

The following evening Caroline Oakley was her designated nurse while Letby was caring for two other babies in Nursery One.

Having gone for a break, at 1.30am the monitor alarm sounded and Oakley was asked to return. Although Baby D recovered quickly, the experienced nurse spotted an unusual rash.

‘The rash struck me,’ she told the court. ‘I had not seen that rash on a baby I had looked after.’

At 3am the crying infant’s oxygen levels fell again, picking up after she was given breathing support. But 45 minutes later she stopped breathing. Resuscitation started, with Letby helping out.

‘We were just standing there, looking at her dying,’ the child’s mother would recall. Baby D was pronounced dead at 4.25am on June 22, the prosecution alleging that Letby had injected air into her bloodstream. ‘Parents devastated, dad screaming,’ Letby later messaged a colleague. ‘Sometimes I think how is it such sick babies get through and others die so suddenly and unexpectedly. Guess it’s how it’s meant to be . . . there’s a reason for everything.’

The doctors on the ward, however, were worried. Baby D’s death was the third in a fortnight. Dr Stephen Brearey, head of the neonatal unit, reviewed their circumstances and Letby’s presence was noted at all the collapses. But no one took the threat seriously at that stage.

Dr Brearey said he even made the remark, ‘It can’t be Lucy, not nice Lucy’ in the meeting when the link was mentioned.

He discussed it with Dr Ravi Jayaram, a paediatrician who has appeared on ITV’s This Morning and the BBC’s The One Show. But it was regarded as ‘an association, nothing more’.

Baby E and Baby F: ‘More of a scream than a cry’

Date of attacks: August 3 and 5, 2015

VERDICT: Guilty of murdering Baby E and attempting to murder Baby F

Identical twins Baby E and Baby F were born ten weeks early at the end of July and placed side by side in Nursery One.

They were doing well, and by August 3 there was talk of the ‘perfect’ boys being moved to a hospital nearer their home. But when their mother went to take some milk to them at 9pm, she heard Baby E screaming and found him with blood around his mouth. ‘It was like nothing I had heard before,’ she would recall.

‘It was horrendous . . . more of a scream than a cry.’ Letby was the twins’ designated nurse and she explained the blood by saying his feeding tube must have been rubbing the back of his throat.

She told the mum to go back to her ward, which she did, saying she trusted Letby ‘completely’.

Baby E was seen by the registrar then and again at 11pm, by which time the bleeding was significant: a quarter of the volume of blood in the baby’s body had been lost.

Baby E deteriorated further and a rash of flitting, purple patches was noted as CPR and adrenaline to re-start his heart were administered.

But it was all in vain and at 1.23am the baby was handed to his parents so they could hold him as he passed away.

Letby put together a memory box and even bathed the boy because his mum was too ‘broken’ to do it herself.

The prosecution alleged Letby had forced a bit of medical equipment such as a rigid wire or suction tube down Baby E’s throat. His mother had interrupted her in the process of murdering him. Letby had finished him off with an injection of air into the bloodstream.

Reeling from the death of one son, the parents wanted Baby F moved to another hospital. But no ambulances were available.

And by that evening Letby was back on shift, caring for another baby in Nursery Two, where Baby F had been moved.

He was doing well and was receiving extra nutrition via a drip. But in the early hours of August 5, his blood sugar dropped, he vomited milk and his heart rate surged. Attempts to raise his blood sugar levels by giving doses of dextrose had little impact.

Indeed, it was only when a decision was taken to stop the nutrient feed that evening that his blood sugars started to stabilise.

Letby was not working that night — instead attending a salsa dancing class.

When blood test results taken from Baby F were returned a week later, they were very unusual, showing very high levels of insulin that could not have been naturally produced in the boy’s body. While one consultant realised the levels were abnormal, the results were not flagged to senior staff.

The prosecution case was that Letby had poisoned two nutrient bags with insulin. Baby F eventually made a full recovery.