"The case has been transferred to the CB-CID and they have taken over the probe," a top police official told PTI.
Thirteen-year-old Dilshan died of bullet injuries yesterday.
Dilshan was allegedly shot at when he tried to pluck some almonds from the premises, housing the residential quarters, and succumbed to injuries at the Government Hospital.
The army spokesperson on Sunday maintained there was no armed guard inside the entire colony, located in the Island Ground locality near the State Secretariat.
The army termed the incident as "very unfortunate," and said it would not allow the guilty to go scot-free.
"We have constituted a board of officers to carry out a proper search of the area including the houses adjoining the scene of the incident. The process of search is going on in detail," Brigadier (administration) Sashi Nair told reporters.
Condemning the killing, Tamil Nadu Chief Minister Jayalalithaa on Sunday said that an army jawan had opened fire on the teenager, who succumbed to injuries in a government hospital.
Jayalalithaa, who ordered a compensation of Rs 5 lakh to the victim's family, said the chief secretary had written to the general officer commanding to hand over the army jawan "who committed this brutal act," to the state police.