The trial for a Manhattan nanny accused of fatally stabbing her two young charges has begun.

In 2012, Yoselyn Ortega, 55, allegedly killed 6-year-old Lulu and 20-month-old Leo Krim, a crime for which her attorney is arguing that she is "not responsible by reason of mental disease or defect."

The trusted protector had worked for Marina and Kevin Krim for about two years when she was reportedly found trying to slit her own throat as the children lay dead in the bathtub.

Now, six years on, the mother who discovered the bodies of her own kids faced Ortega as she testified in court Thursday.

She grew emotional as she recounted how she entered her unusually quiet upper west side apartment and found the lifeless bodies of her two "best friends."

Before stepping down from the witness stand, Krim angrily shouted at Ortega: "You're gross! You're disgusting!" 

Ortega faces two counts of first-degree murder and two counts of second-degree murder. If convicted, she faces life in prison.

Following the deaths of the children, the Krims launched a charity, the Lulu & Leo Fund, to raise money for children's art programs. The fund's Facebook account often posts updates about the Krims and their family.

A year after witnessing that horror, she and Kevin Krim welcomed another child, Felix, in October 2013. The couple has another daughter, Nessie, who was 3 at the time of the murders.

"With each new baby, we feel a special and closer connection to Lulu and Leo, who are a constant presence in their siblings’ looks, gestures and voices," the couple wrote on Facebook.

More recently, the couple posted a video message asking people to mention the fund as their case becomes news again as a means of turning the tragedy into something constructive.

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