Officials engaged in the probe are looking at all angles, including sabotage.

There are many questions that the CBI will have to find answers to - was the weather warning issued, was the chopper properly checked before it took off, was it carrying an Emergency Locator Transmitter (ELT) and whether there were any lapses on the part of pilots or Air Traffic Control staff in responding to the requests of the crew for help.

The Cockpit Voice Recorder (CVR) recovered from the wreckage is yet to be decoded.

YSR, as the chief minister was popularly known, his special secretary, chief security officer and two pilots were killed Sep 2, an hour after the chopper took off from Hyderabad for Chittoor district. YSR was to launch a mass contact programme at Chittoor.

The helicopter crashed in bad weather minutes after it lost contact with Air Traffic Control at 9.12 a.m. The severely burnt bodies of the victims were found with the wreckage 24 hours later.

The ground search operation involved over 5,000 personnel of the army, paramilitary forces, police and even tribals living in the forest.