The woman, identified as Uma Sharma, is the relative of a secretary in Civil Aviation ministry, was stabbed at least 13 times with a kitchen knife and there were at least seven other incision marks om her body.
The incident came to light around 3.45 PM when the juvenile, a native of Bihar who was hired by the family on reference of a close relative around two months ago, allegedly ransacked the house and raised an alarm claiming that Sharma was killed by robbers, a police official said.
Sharma and the domestic help were alone at the time of the incident.
Both her son and daughter are settled abroad and her husband, Pramod Sharma, who is a retired engineer, had left home around 2.30 PM for some work, the official said.
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"It is a heinous crime.
The boy has been apprehended and he is being questioned.
We shall urge the juvenile justice board that he be treated as an adult under the new law," Joint Commissioner of Police (Southwest) Dependra Pathak said.
When he was subjected to intensive interrogation, he confessed to the crime, said a police official.
The boy, who shall turn 18 years in another 5 months, told police that his employers often physically assaulted him.
Even today morning, Sharma had allegedly slapped him after an argument over cooking lunch.
He told police that he wanted to take revenge and had hatched a plan around two days ago.
He attacked Sharma after he found her alone this afternoon and had planned to leave the city by the night, the Official said.