Story highlights Nothing appeared amiss between the nanny and children, a resident says

The mother returned home to find the crime scene in a bathroom

The family vacationed with Ortega in her native Dominican Republic

The slain children were 2 and 6 years old

The New York nanny suspected in the killings of two children in her care began knifing herself when their mother entered the bathroom and saw the bodies in the bathtub, police said Friday.

"We believe now that the nanny began to stab herself as the woman entered the room," Police Commissioner Ray Kelly told reporters in a revised account of Thursday's events.

"We initially thought that had already been done but now information is coming out that she did it as the mother entered the bathroom."

Earlier, police had said that Marina Krim found nanny Yoselyn Ortega, 50, on the bathroom floor of the family's Upper West Side luxury apartment with self-inflicted wounds.

In the tub lay the clothed bodies of two of Krim's children: Leo, who had recently celebrated his second birthday with "Pinkalicious-inspired cupcakes;" and his 6-year-old sister, Lucia, who had performed "beautifully in her ballet recital" in May.

Both children had been repeatedly stabbed, police said.

Ortega started stabbing herself in the neck with a kitchen knife, police said. Her wrists were slit.

"The charge is still to be determined," Kelly said.

Krim had left the two children with the nanny, known as "Josie," to take her third child, 3-year-old Nessie, to a swim lesson at a nearby YMCA, Kelly said. She had expected to meet the nanny at a dance class for the 6-year-old around 5:30 p.m.

When the nanny and children didn't show up, Krim went up to the apartment, where she found the lights were off, police said. Krim then returned to the lobby and asked a doorman whether he had seen her two other children leave with the nanny; he had not.

"There comes a time when she goes looking for her children and enters the bathroom and finds her 6-year-old daughter and son stabbed to death in the tub," Kelly said.

That's when neighbors heard a scream.

Leo, left, and Lucia Krim were discovered dead in a bathtub by their mother.

The children's father, Kevin Krim, a senior vice president for CNBC Digital and former Yahoo executive, was en route back home from the West Coast. Police broke the news to him at John F. Kennedy International Airport.

"A member of the CNBC family has suffered an unimaginable loss," NBC Universal said in a statement. "The sadness that we all feel for Kevin, Marina and their family is without measure."

The nanny was taken to a hospital, where she was in critical but stable condition.

The bodies of the two children were removed from the building on a single stretcher and taken to a hospital where they were pronounced dead.

Ortega was heavily sedated and under police watch on Friday at Weill Cornell Medical Center, said Deputy Police Commissioner Paul Browne.

Kelly said she was breathing with the aid of a tube and unable to talk.

A native of the Dominican Republic, Ortega had been a naturalized U.S. citizen for 10 years.

Friends had introduced the family to Ortega, and she had worked for them since Leo's birth two years ago, police said.

She lives at another address on Manhattan's West Side with her son, her sister and her niece, Kelly said.

"We're just grieving. Worst nightmare anyone could ever imagine," said grandmother Karen Krim, who lives in California. "We don't have a clue what set her off."

Police on Thursday evening escorted from the apartment building the mother and her 3-year-old daughter, covering them with a white sheet to shield them from photographers and gawkers. The mother was treated at a hospital for trauma, police said.

Less than an hour before the killings, Charlotte Friedman rode in the elevator with the nanny and the youngsters.

"I told the little girl 'do you know how beautiful you are?' and she gave me the biggest smile I've ever seen and said 'thank you,'" Friedman said.

Nothing seemed amiss with the nanny or the children, she said.

Later, Friedman was back in the elevator -- heading out to run errands -- when she heard a "primal scream" from somewhere in the building.

"It was pure terror," she said. "...It was unlike anything I've ever heard before."

She isn't sure who she heard scream. But after she got off the elevator, Friedman saw the youngsters' mother screaming on the mezzanine.

News of the crime spread quickly. Some parents in the neighborhood said they rushed home to hug their own children.

Maryellen Conway, 39, a mother of two, said she called her children's nanny and they cried together. "She was in tears. I trust her, obviously, with my life and she's part of our family," Conway said. "There's no words to describe what they're going through."

On Friday morning, Jasmarin Rothbarb was pushing a stroller near the Krims' apartment building. She said she employs a nanny, but the killings have made her question whether to continue.

"It's a tough call," she said. "You trust these people with your most precious joys. I think I see more mothers out today than nannies. It's a horrible thing."

Outside the building, Kathleen Peters placed flowers at a makeshift memorial. Peters, a mother herself, also works as a nanny for children who live a few blocks away. "It makes me really, really sad," she said. "I can't understand why (the nanny) would do something like that."

The apartment is a block west of Central Park and four blocks south of the American Museum of Natural History, two locations popular with nannies.

It is not unusual for their employers to treat nannies as extended members of their own families. That was the case with the Krims. Marina Krim's blog, "Life with the Little Krim Kids," offered the loving mother's view of a family life that included Ortega as a member.

Last February, the Krims traveled to the Dominican Republic, where they met their nanny's family.

"We spent the past nine days in the Dominican Republic," Marina Krim wrote on February 18. "We spent half the time at our nanny, Josie's sisters home in Santiago and the rest at Balcones de Atlantico in Las Terrenas, a condo-style hotel where the 'Real Housewives of Dominican Republic' and their families hang on weekends. It was wonderful."

She added, "We met Josie's amazing familia!!! And the Dominican Republic is a wonderful country!!"

One photograph showed the families together, the nanny holding the girl who was learning how to swim at the time her siblings were killed.

The blog included hundreds of photographs and notes about picking blackberries, celebrating birthdays, going to a pumpkin patch.

On September 30, Marina Krim posted a photograph of her son after his second birthday. The boy had a mischievous look as he played at a toy kitchen set. "Leo 'Lito' Krim!!!!! Yes, the 2 year old boy," his mother wrote. "One of the best parts of my day is after I drop both girls off at school and have 3 precious hours with little Lito all to myself. Ok, I'm near getting cheesy I adore this boy so much!!!"

Weeks before his birthday, mom and son walked home, with the lad pointing at toy cars, trucks and fire engines, excited in anticipation of his birthday. "Mama, present, present," he said after spotting a toy helicopter.

"Lito, I must say, is a very clever little boy," she wrote. "He is super talkative and just has a million thoughts running through his brain and can express himself amazingly well for an almost-2 year old."

In April, 6-year-old Lucia, known as Lulu, accompanied her father on a take-your-child-to-work event. On the whiteboard in her father's office, she wrote: "I like your ofis Dada. Love LuLu."

Marina Krim logged her final entry at about 2:30 p.m. Thursday, three hours before the killings were discovered.

"Leo speaks in the most adorable way possible. Firstly, he speaks super clearly, so you can understand every word (he) is saying. And he does things like, 'I want a fresh bagel' and 'Dito (what he calls himself) wants cold milk' and most adorable of all, 'No thank you' -- he never uses 'No' alone, it's always paired with 'thank you.'"

Within hours of the killings, hundreds of people had left messages of condolences on the blog; by Friday morning, it had been taken down.