Children’s coats on a rack by the door. A child’s drawing on the wall. A stroller and a pink knapsack in the living room. A scarf with droplets of blood. Blood stains on the walls along the narrow hallway. A knife wrapped in a towel on top of a toy refrigerator.

The images, in photographs taken by a crime scene detective and presented on Tuesday in State Supreme Court in Manhattan in the trial of Yoselyn Ortega, provided a first public look inside the Upper West Side apartment where prosecutors say she killed two young children in her care five and a half years ago. Ms. Ortega, the children’s nanny, is accused of fatally stabbing the siblings, nearly decapitating them and leaving them to bleed to death in a bathtub.

The crime scene detective, Carlos Pantoja, said he took the photos inside the three-bedroom apartment shortly after midnight, nearly seven hours after the children’s mother, Marina Krim, found them mortally wounded and saw Ms. Ortega stabbing herself in the neck.

Testimony in the trial began last week, with Ms. Krim telling the jury of her harrowing discovery that day in 2012. This week, jurors have seen some of what Ms. Krim saw, as prosecutors have presented photos from the crime scene, along with testimony from some of the emergency medical workers and police officers who responded to the apartment.