At least 100 Naxals are suspected to be involved in the attack in which a BJP MLA and four security personnel were killed in Chhattisgarh's Dantewada district, a police official said on Wednesday.
Police have also recovered a GPS device of Naxals from the site in which the rebels had set the location of the Improvised Explosive Device (IED) used in the incident.
Bheema Mandavi, the BJP MLA from Dantewada seat, and four personnel of his security staff were killed when Naxals blew up their vehicle near Shyamgiri village on Tuesday, just two days before the first-phase of the Lok Sabha polls in the state.
"We have received inputs that around 100 Naxals, including 50 to 60 armed and rest militia (lower rung) members, led by commanders Deva and Vinod, were involved in the attack," Dantewada Superintendent of Police Abhishek Pallava told PTI over phone.
Malangir area committee of the banned CPI (Maoist), which is active in the area, along with Kerlapal area committee and some cadres of Jagargunda area committee jointly executed the attack, he said.
Three weapons, including a 9 MM pistol and two rifles, were reported to be missing from the attack site, he said.
"According to ground inputs, it was a pre-planned attack as a large number of armed cadres could not gather in such a short span of time. It could have been a trap laid for the MLA," Mr Pallava said.
On Tuesday, it was Mandavi's third visit on the route in the election season.
The SP said the area was sanitised twice by the District Reserve Group (DRG) in last five days, but the IED can be planted in a day only.
On Monday, Mandavi passed through the same route but that day, de-mining exercise was done by security forces and he was escorted by an additional team of DRG, Mr Pallava said.
That day, the MLA is suspected to have told some villagers that he would attend the fair held in Shyamgiri on Tuesday, or somebody from the village would have invited him for it, he said.
"We are checking the call details record of the MLA to ascertain if any person from the area called him," he said.
The MLA's mobile phone is missing and it might have been taken by Naxals, the official said.
On Tuesday also, Mandavi was being escorted by additional security of 50 DRG personnel on 25 motorcycles, during his poll campaigning.
But when he sought that security be withdrawn citing that he had completed his campaigning for the day, the security forces returned, he said.
The MLA then suddenly decided to head to towards Kuwakonda in his bullet proof vehicle, following which his security staff in the escort vehicle informed the police.
The Bacheli police station head officer immediately called the MLA, asking him not to take that route due to security reasons, he said.
"In the meantime, the MLA left behind his piloting escort vehicle. He, along with four security personnel in his SUV, and another vehicle behind carrying five policemen, headed towards Shyamgiri, ignoring the advisory," he said, adding two escort vehicles followed his SUV.
After spending a couple of minutes at Shyamgiri fair, the MLA headed towards Kuwakonda.
He barely covered a distance of around 200 metres when Naxals triggered a powerful IED blast with around 60-70 kg of landmine, that flung the vehicle several feet in the air. The blast left an eight-feet crater at the site, he said.
"All the vehicle occupants, including the MLA, his three personal security officers and the driver - a police constable, died on the spot," he said.
The Naxals also opened fire on the vehicle, to which the security personnel in the escorting vehicles retaliated.
About 25 minutes after the blast, reinforcement reached the spot and till then, intermittent exchange of fire was underway, the official said.
Soon after sensing the presence of reinforcement, the rebels fled in three different directions, he said.
The distance between Bacheli and Kuwakonda in 14 km and the strike took place four km ahead of Kuwakonda police station.
A GPS device belonging to Naxals was also recovered from the spot in which the location of the IED planted beneath the road was set, Mr Pallava said.
The GPS was being examined to check if locations of more IEDs planted in the area were fed into it, he added.