The boy fell into the borewell around 5.30 p.m. on Friday and got stuck at 30 feet and rescue efforts began soon after that.
Later that night, he fell further down to about 90 feet.
Speaking to reporters in the wee hours of Tuesday, J. Radhakrishnan, Principal Secretary, Revenue Administration, Disaster Management and Mitigation department said bad foul started emanating from the borewell and the medical teams also confirmed the death.
The body that started decomposing was taken out and sent for postmortem.
According to officials, the borwell, and also the hole drilled near it to rescue the boy, will be closed soon.
On Saturday, the National Disaster Response Force and State Disaster Response Force took over the rescue operation as other techniques used to take the boy out of the borewell have failed.
Initially, earthmoving equipment was pressed into service to dig a pit near the borewell to reach the boy. But, it was stopped midway as the terrain was rocky. Besides, it was felt that this process could cause vibrations that may loosen the soil inside the borewell, thereby slipping the boy further down.
Later, the rescue team used a special equipment 'borewell robot'. But that too was not successful.
( With inputs from IANS )