The mother told authorities that she watched helplessly as the animal invaded their home over the weekend in a village in Banki, Odisha, and took her days-old son, according to Agence France-Presse.
"She raised an alarm but the monkey quickly leaped over the roof and vanished out of sight," police sub-inspector S.M. Baral told the news agency.
After an emotional day-long search for the child, he was found dead Sunday in a well behind the home, where authorities and the child's parents suspect the animal may have dropped him, according to the AFP.
"It seems while the monkey was jumping from the terrace my baby somehow slipped from its clutches and fell in the well," the child's father, identified as Rama Krushna Nayak, told the Times of India.
Authorities called it "a very rare case," telling BBC News that monkeys in the area have been known to damage personal property but not take people.
"While monkeys attacking humans or entering houses in search of food are fairly common, this is the first case in which one has run away with a baby," police officer PC Pradhan told the network.
Police said a woman discovered the baby's body as she was getting water from the well, then alerted family members, who helped pull him from the ground. An autopsy revealed that the child had died from asphyxia because of drowning, according to local news reports.
Police told the AFP that the "family is convinced it's the monkey that killed their child."
Baral told the news agency, "Since there were no injury marks on the baby, maybe the monkey dropped him in the well."
The monkey accused of taking the child was identified as a rhesus macaque, or Macaca mulatta, a species with reddish-pink faces and rear ends that can weigh up to 27 pounds, according to National Geographic.
The rhesus macaque, a well-known species of Old World monkeys, is native to Central South and Southeast Asia and, oftentimes, lives close to humans.
In India, Hindus consider these monkeys sacred and leave them alone, according to National Geographic, even though the animals are known to attack people and destroy property in search of food.
Protesters recently blocked a road in Cuttack, a city in Odisha, to express dismay about monkey attacks in the area, according to the Hindustan Times.
After numerous monkey attacks last year in a village in the Kendrapara district of Odisha, one government employee died of his injuries, and schools and health-care facilities had to shut their doors, according to the Hindustan Times. And the newspaper said that over the past couple of weeks, several women in a village in Odisha have suffered injuries in similar attacks.
Authorities are still searching for the monkey suspected in the newborn's death.
(Except for the headline, this story has not been edited by NDTV staff and is published from a syndicated feed.)