Viktoria Ivanova had not long given birth to her baby boy, named Volodya, when Alina Araslanova reportedly walked over to her hospital bed, grabbed the newborn and threw him out of the third floor window for no apparent reason.
Volodya hit the ground and died instantly, at not even a day old.
The incident happened on Monday in Sterlitamak, Russia, and Araslanova had also given birth earlier in the evening to a baby girl.
Russian news outlet, NTV, reports that the mums were lying on beds next to each other on the maternity ward.
The babies were then brought in for feeding when Araslanova allegedly tossed the baby to his death.
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Araslanova has since undergone a further psychiatric examination to decide whether she will be arrested or sent away for treatment.
Her children have been removed and remain in the care of the authorities.
Police are continuing to investigate the tragic incident. The Investigative Directorate said in a statement: “At present, a number of investigative and operational measures has been started to establish all the circumstances of the crime, as well as the reasons and conditions that led to it.”
Additional reporting by Melissa Veitch.