The New York nanny who murdered two young children at an Upper West Side apartment must have gone insane, the grandmother of the children concluded.

"My daughter-in-law, if she thought there was anything wrong, she would have never left the two with her. This had to be something simmering inside this woman. Obviously, she went insane," Karen Krim told the New York Daily News.

According to the local publication, the nanny, Yoselyn Ortega, was treated like family by the Krims which thus added to the shock of the tragedy.

Ortega, known as "Josie," stabbed a 2-year-old boy and 6-year-old girl with a kitchen knife on Thursday. The mother, Marina Krim, found the children in the bathtub of her apartment and the nanny stabbing herself on the bathroom floor. She screamed so loudly that neighbors called 911.

Krim had taken her 3-year-old daughter to a swimming lesson and was scheduled to meet the nanny at a dance studio afterward, according to The New York Times. But when they didn't show up, Krim went to the apartment, near Central Park, and discovered the bloody nightmare.

The children were pronounced dead at the hospital. Ortega, who is from the Dominican Republic, was in critical but stable condition.

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The motive behind the murders is still a mystery.

Jasmarin Rothbarb said to CNN on whether she'd continue to use a nanny, "It's a tough call. You trust these people with your most precious joys. I think I see more mothers out today than nannies. It's a horrible thing."

The Krims have been described as a perfect and beautiful family. The father, Kevin Krim, is an executive at CNBC which released a statement Friday expressing sadness over the loss.

"Our thoughts, prayers and unwavering support are with them all," CNBC stated. The company arranged for the Krims to stay at a hotel after leaving the hospital.