A nanny has been found guilty of murdering two children she stabbed at their luxury New York City apartment.

Yoselyn Ortega had pleaded insanity, but the jury rejected that defence as they unanimously convicted her.

The bloody bodies of Lucia “Lulu” Krim, six, and her brother Leo, two, were found by their mother in a bathtub at the Manhattan flat on 25 October 2012.

Marina Krim told the court how she saw Ortega, 55, stabbing herself in the neck in an apparent suicide attempt.

She had come home with her third child, three-year-old Nessie, after Ortega did not turn up at Lulu’s dance class.

Ms Krim was found by police crying and screaming hysterically, clutching on to her surviving child.

After two days of deliberations, the jury found Ortega guilty of four charges: two counts of first-degree murder and two counts of second-degree murder, which are punishable by a maximum sentence of life in prison.

Prosecutors said the nanny was disgruntled because she felt she was being overworked by the family at the Upper West Side apartment.

Ortega was also struggling to pay tuition fees for her 17-year-old son, whom she had brought to the US from the Dominican Republic and enrolled in a private school.

The nanny’s defence team argued she suffered from “chronic mental illness” and was mentally incapable of being held responsible for her actions. Her lawyer said she had hallucinated an order from the devil “to kill the children and herself”.

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However, the prosecution said Ortega’s actions were premeditated and the trial heard how she slit Leo’s neck from behind so he would not fight back as his sister had done.

“We hope now that this verdict will give the Krim family an opportunity to heal, to find some closure and to move on in their lives,” Manhattan District Attorney Cyrus Vance told reporters following the verdict.

Kevin Krim, the children’s father, stood beside the prosecutor with tears in his eyes but declined to comment. He was returning from a business trip at the time of the 2012 killings.