London: A British nurse who described herself as a "horrible evil person" was found guilty on Friday of murdering seven newborn babies and trying to kill another six in the neonatal unit of a hospital in northwest England where she worked.

Lucy Letby, 33, was convicted of killing five baby boys and two baby girls at the Countess of Chester hospital and attacking other newborns, often while working night shifts, in 2015 and 2016.

The verdict, following a harrowing 10-month trial at Manchester Crown Court, makes Letby Britain's most prolific serial child killer in modern history, local media said.

She was found not guilty of two attempted murders while the jury, who spent 110 hours deliberating, were unable to agree on six other suspected attacks.

"We are heartbroken, devastated, angry and feel numb, we may never truly know why this happened," the families of Letby's victims said in a statement.

Prosecutors told the jury Letby poisoned some of her infant victims by injecting them with insulin, while others were injected with air or force fed milk, sometimes involving multiple attacks before they died.

"I killed them on purpose because I’m not good enough to care for them," said a handwritten note found by police officers who searched her home after she was arrested. "I am a horrible evil person," she wrote. "I AM EVIL I DID THIS".

Some of those she attacked were twins - in one case she murdered both siblings, in two instances she killed one but failed in her attempts to murder the other.

The youngest victim was just one-day old.

'Malevolent presence
Letby will be sentenced on Monday and faces a lengthy prison term, possibly a rare full life sentence.

Her actions came to light when senior doctors became concerned at the number of unexplained deaths and collapses at the neonatal unit, where premature or sick babies are treated, over 18 months from January 2015.

With doctors unable to find a medical reason, police were called in. After a lengthy investigation, Letby, who had been involved in the care of the babies, was pinpointed as the "constant malevolent presence when things took a turn for the worse", said prosecutor Nick Johnson.

Pictures of Letby on social media portrayed a happy and smiling woman with a busy social life, and in one photo she was seen cradling a baby. But, during months of often distressing evidence, her trial heard she was a determined killer.

The jury was told how Letby had tried on four occasions to murder one baby girl before she finally succeeded. When another of the victim's mothers walked in on her attacking twin babies, she said: "Trust me, I'm a nurse".

At her home after her arrest, detectives found paperwork and medical notes with references to the children involved in the case. She had also carried out social media searches for the parents and families of the murdered babies.

Letby wept when she gave evidence over 14 days, saying she had never tried to hurt the babies and had only ever wanted to care for them, blaming unsafe staffing levels on the ward and its dirty conditions.

She also claimed four doctors had conspired to pin the blame on her for the unit's failings and had written the "I am evil" message because she had felt overwhelmed.

Cruel liar
But the prosecution said she was a cold, cruel, calculating liar who had repeatedly changed her account of events and her notes should be treated as a confession.

Detectives said they had found nothing unusual about Letby's life and could not determine any motive. "Unfortunately, I don't think we'll ever know unless she just chooses to tell us," said Detective Superintendent Paul Hughes who led the investigation.

One senior doctor at the neonatal unit, Stephen Brearey, told the BBC that hospital bosses had failed to investigate allegations against Letby and failed to act on his and his colleagues' concerns.

"Our staff are devastated by what has happened, and we are committed to ensuring that lessons continue to be learned," said Nigel Scawn, medical director at Countess of Chester Hospital NHS Foundation Trust.

The government said it had ordered an independent inquiry which would include how concerns raised by clinicians were dealt with, while the father of twins who survived her attempts to kill them demanded answers from the hospital.

"They could have stopped it," said the father, who cannot be named for legal reasons.

Police are carrying out further investigations into all the time Letby had worked as a nurse at the hospital and at another one in Liverpool where she had trained, to identify if there were any more victims.

"There is a number of cases that are active investigations that parents have been informed of," Hughes said.