Two days after a powerful explosion killed 15 civilians and 16 security force personnel travelling in a bus in Chhattisgarh, investigators have established the sequence of events leading up to Monday's tragedy.

On May 16, 104 Koya Commandos (a special wing of SPOs), led by Sukma SHO Sandeep Chandrakar, left Sukma for a combing operation in the jungles surrounding Bhusaras. At Bhusaras, the Koyas were joined by 24 members of the Special Task Force of the Chhattisgarh Police.

While officials refused to divulge the results of the one-day operation; newspapers reported that security forces killed two Maoists in Goomiapal village in the Kirandul area on the same day. Kirandul is about a day's march from Bhusaras.

In a report on CGnet Swara - a telephonic Adivasi news service - Gujju Bai, the sarpanch of Goomiapal, claimed that the two Adivasis killed by the police were innocent.

In the evening of May 17, the police emerged from the forest at Bhusaras. "We normally enter the forest from one route and exit from another," said a member of the team, "This time we decided to take the same route out." At about 4:30 p.m., the exhausted commandos stopped a bus carrying civilians from Dantewada to Sukma. About 15 uniformed and armed commandos got into the bus, while another 15 climbed onto the roof.

Soon after, the remaining commandos commandeered two private trucks and a Mahindra Max jeep and followed the bus to Sukma. On seeing the approaching bus, a team of Maoists led by Ravula Srinivas, alias Ramanna, Secretary of the South Bastar Regional Committee of the CPI (Maoist) triggered the blast at a spot about 4 km. from Bhusaras.

In a telephone conversation with this correspondent, Ramanna claimed that the blast was in response to the alleged killing of villagers in Goomiapal, Gompad and other villages by security forces.

Investigators believe that the mine was probably planted one or two days before the incident. Four days prior to the incident, the Chhattisgarh police had conducted extensive de-mining operations on the very same stretch of road.

In the Chhattisgarh countryside, roads are built on embankments about eight to ten feet above the ground. This gives the road a stable foundation and protects it from flooding. Leaving the tarmac top intact, Maoists planted the mine by digging a hole into the side of the embankment, about six feet below the surface of the road.

The blast was triggered by a Maoist hiding behind a check-dam about 250 metres from the road.

Last month, a Maoist explosives expert told this correspondent that high intensity blasts are usually triggered using a modified camera flash powered by four 1.5 Volt batteries. The flash provides the immediate surge of electricity necessary to detonate powerful bombs from a safe distance.

Police confirmed the recovery of about 350 metres of aluminium wire and a plastic socket into which the flash-trigger would have been plugged.

As reported on Tuesday, spent shells recovered from the dam indicate that the Maoists fired upon SPOs struggling to escape the charred bus.

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