Kaleeswari (24) was walking towards the bus-stand, carrying her son when two persons, wearing helmets on a motorcycle, snatched her gold chain, they said.
When the woman started screaming, the culprits snatched the baby and threatened to kill him if she did not remain silent, they added.
They then sped off with the baby to throw it in a well, police said, adding, efforts to save the child were futile and its body was retrieved later.
An alert has been sounded in and around the area to nab the culprits, police said.
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