Yoselyn Ortega was born in 1962 in Santiago de los Caballeros, Dominican Republic. She immigrated to the United States and became a naturalized citizen. Prior to the murders, Ortega had been employed by the Krim family for approximately two years as a nanny for their three children: Lucia (6), Leo (2), and Nessie (3). She was introduced to the Krims through a family friend and came highly recommended.

Ortega lived in the Hamilton Heights neighborhood of Manhattan with her 17-year-old son, her sister, and her niece. She was reportedly experiencing financial difficulties and had requested additional work from the Krim family to supplement her income.

On October 25, 2012, Marina Krim returned to her Upper West Side apartment after taking her daughter Nessie to a swimming lesson. Upon entering the bathroom, she discovered her two other children, Lucia and Leo, in the bathtub with multiple stab wounds.

Ortega was found in the bathroom alongside the children, having inflicted severe stab wounds upon herself in a suicide attempt. She survived her injuries and was arrested at the scene.

During the trial, the prosecution argued that Ortega acted out of resentment and jealousy toward the Krim family. The defense claimed that she suffered from untreated mental illness, leading to the tragic events. However, the jury found her guilty of two counts of first-degree murder and two counts of second-degree murder on April 18, 2018.

On May 14, 2018, Yoselyn Ortega was sentenced to life in prison without the possibility of parole. During the sentencing, Judge Gregory Carro referred to her actions as "pure evil."

In the aftermath, Marina and Kevin Krim established the Lulu & Leo Fund, a non-profit organization dedicated to supporting creative programs for children and families.