Story highlights Investigators have ordered the woman undergo psychological evaluation

Moscow police say they believe the woman killed the child, whom she was babysitting

The child was believed to have been 3 or 4 years old

(CNN) A woman who carried the severed head of a child into a Moscow metro station Monday has been arrested, the city's prosecutor's office said.

Moscow police said they believe the woman killed the child, whom she was babysitting. The child was believed to have been 3 or 4 years old.

According to preliminary information released by the Russian Investigative Committee, the woman waited until the parents of the child left an apartment with their older child, then killed the child, set the apartment on fire, and fled the scene.

The body of a child, which showed signs of a violent death, was found after firefighters put out the blaze.

A motive for the killing was not clear; the investigation is ongoing.

Read More