Police said they were searching for the culprit based on interrogation of a neighbour of the deceased child.
The toddler's 22-year-old mother P Malliga, separated from her husband, used to leave her child with the woman everyday while going for work. Yesterday, when Malliga returned from work to take her child home, she found her daughter dead.
The woman told Malliga that the child had died due to severe fever.
Later when she took the baby to a hospital, doctors found she had been sexually assaulted, police said.