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The nanny who knifed to death her two young charges has been handed a life sentence amid emotional scenes at a Manhattan court.

Onlookers cried as Yoselyn Ortega was given the maximum sentence with no possibility of parole after she fatally stabbed Lucia (Lulu) Krim, 6, and brother Leo, 2, in the bathroom of their family's luxury apartment in New York's affluent Upper West Side.

Her insanity plea was rejected and she was convicted on two counts of first-degree murder on April 19.

"I hope that no one goes through what I have"

Judge Gregory Carro today said the "tragic case" could only be summed up as "pure evil", sentencing Ortega to the maximum punishment of 25 years to life for both counts, to run consecutively.

He noted that she had meticulously planned her suicide, but no one knew when she decided to kill the children too, because she would not say.

Ortega wore a long-sleeved grey top, black pants and glasses, her hands cuffed and hair tied back, as she learnt her fate at Manhattan Supreme Court. She spoke briefly before the result to ask the forgiveness of God and the children's parents, adding: "I'm very sorry for everything that happened but hope that no one goes through what I have gone through."

"Although many wish me all the worst, my life is in the hands of God. I am in jail but perhaps there are many more in prison than I am."

She said she had told her family she felt unwell, and had told her employer Marina Krim she had an appointment, but had not been allowed to go because Mrs Krim also had an engagement.

Ortega hung her head but did not cry as the children's sobbing mother lashed out at her for showing "not an ounce of remorse" and setting out to "destroy and ruin" her family.

She said the defendant had deliberately avoided her on the day of the murders, and sought an opportunity to kill the kids.

"Raw pain" over "terrible violence"

A distraught Mrs Krim said she had not intended to return to court after a gruelling six-hour testimony during the trial, which she felt had "expressed a lot of my rage." But she said she was "here to finish a horrible chapter in my family's life."

Lulu and Leo were "powerful forces" and were "two stars now that will always lead us forward", she said, in a heartbreaking tribute to her lost children.

"I still remember how in love I felt when looked at my son's deep brown eyes," she said.

"Nessie will never know what her sister and brother are like. Each time she makes a wish, it's always for Leo and Lulu to come back to be with us. Nessie knows this wish will never come true."

She lashed out at Ortega's "entire family of unethical people", who she said had contributed to the terrible crime by lying about the 55-year-old's nannying credentials and experience and never taking responsibility.

Her husband Kevin thanked the jurors, court officials and New York Police Department and said the family would mourn Lulu and Leo "for the rest of our lives."

Mr Krim accused Ortega and her family of showing complete "disregard for morals, ethics or basic human decency" and called her a "malignant narcissist" who had never shown any sign of remorse.

He said she had refused plea bargains, which he did not believe she deserved, because she had wanted to put them through the pain of this trial.

He called Lulu "our little Buddha", saying she was a natural teacher who loved taking care of people. "She had energy in her soul that was magnetic," he added.

He said Leo was "dreamy" and the couple was "madly in love with him."

"We miss him so much," he said. "Marina and I are heartbroken and we know you share in our raw pain.

"We are certainly distraught over how they died, the terrible violence."

Death in the family bathroon

Mrs Krim told Manhattan Supreme Court during the trial of how she started to panic when she could not find Lulu at the dance class where her nanny had been due to drop her off on October 26, 2012. Mrs Krim had taken her third child, Nessie, to a swimming lesson.

Unable to contact the 55-year-old nanny, the paediatrician rushed home, where Ortega was supposed to have taken Leo for a nap.

The worried mother arrived to every parent's worst nightmare — the gruesome sight of her dead children in a bathtub, blood everywhere, and a kitchen knife dumped in the sink. Ortega, a US citizen originally from the Dominican Republic, had stabbed Lulu 30 times.

Police arrived to ghastly scenes, and Ortega lying on her back in the bathroom with a self-inflicted stab wound to the neck

Jurors gasped in horror as graphic images of the crime scene were shown in court. There was evidence of a struggle as Lulu tried to fight off her nanny.

"Get me out of here. Please, get me out of here. Get me out!"

Her husband Kevin Krim told Manhattan's Supreme Court he heard about the murder when he switched his phone off aeroplane mode at John F. Kennedy International Airport in New York to find a barrage of text messages from concerned friends.

The former CNBC executive said he was trying to figure it out and "fumbling around" when a flight attendant asked him to go to the cockpit. "It's the worst thing imaginable. I was hoping it was a nightmare, and it wasn't," said Mr Krim.

He said two plainclothes police officers had to pick him up off the floor, somebody grabbed him by the arm and somebody took his bag. He said he kept asking "What's going on?" and then saw he had a voicemail from his wife.

"I pressed play to listen to it, and I just heard the background noise of screaming," he testified. "I crumbled to the ground."

Ortega had pleaded not guilty on the grounds on the grounds of mental illness, but New York courts have a high bar for proving insanity, with jurors deciding she was aware of what she was doing.

She claimed she did not remember the attack and was possessed by the devil, but a psychologist told jurors she was depressed, but not mentally ill — and had not mentioned hallucinations at the time.

Her sister Celia said the nanny had "snapped" after neighbours revealed she had been visibly unravelling in the months before the sickening murder.

"She lost a lot of weight. She looked very unhealthy. It looked like she was going through some problems," Ruben Diaz told the New York Post. "She had aged a lot — like seven years in a few months."

The nanny had previously complained that Mrs Krim was too demanding and she was upset at being asked to do housework on top of childcare in her $24-an-hour job.

"I had to do everything and take care of the kids," she told police after the brutal murder.

Prosecutors said Ortega was driven to kill because she was jealous of Ms Krim and resentful of the cleaning she had to do.

Mr Krim, who now works at a start-up, and his wife use a Facebook page to post updates on their lives. They went on to have two more children, Felix born in 2013 and Linus in 2016.

The couple started the Lulu and Leo Fund, which aims to support innovative art programs for children. They recently posted a video message on Facebook asking that people mention the fund when their case is in the news.