Jharkhand police on Monday began an investigation into the killing of Jharkhand Mukti Morcha parliamentarian Sunil Mahato amidst suspicions of a conspiracy behind the act and launched coordinated combing operations with their counterparts in West Bengal to track down his assailants.

"The police have filed a complaint against unknown persons after a police team visited the site (Bakuria)," said East Singhbhum Police Superintendent Pankaj Darad.

He, however, could not give the exact figure of the persons against whom the complaint had been filed. He replied in the negative when asked whether the investigating team had got any lead into the gunning down of the 38-year-old, who represented Jamshedpur Lok Sabha constituency, at Bakuria, about 40 km from Jamshedpur.

Jharkhand Director General of Police Devi Mahapatra said, "I feel it is some kind of a conspiracy because Sunil Mahato was made to stay back for the women's football match organised there. He was told it would get over in 15 minutes, which is not possible. I feel it is some kind of conspiracy."

Chief Minister Madhu Koda told media persons in Jamshedpur that the CBI probe into the killing of Mahato was recommended to find out whether there was any conspiracy angle to it.

"The CBI inquiry has been recommended to find out the conspiracy angle, if any, why the football match organised on a holiday and whether there was a security lapse," Koda said.

The DGP said Mahato's assassination was not due to 'security lapse' as police did not have any prior information about his visit to the venue of the football match. The question of security lapse will arise only if the police had prepared for it.

Madhu Koda also cited revenge by Naxals as another possible reason for the killing of Mahato and said investigators will probe this angle as well.

"We cannot deny this (revenge killing). But Naxals always target the powerful like Parliamentarians, legislators and government employees. This is a pre-planned attack," Koda said when asked whether it was a case of revenge killing in the wake of the government's recent action against Naxalites.

On December 15, two Naxalites -- one hailing from Ranchi and another from Jamshedpur -- were killed in a police encounter at Bagdubi in West Bengal's Bankura district. On March one, there was an encounter at Singhbum in Jharkhand but there were no casualties. Police also got success against Naxalites in Hazaribag and Palamau recently, Koda added.

Most of the areas in east and West Singbhum districts, infested by Naxalites, have been witness to some of the worst Naxal-related incidents in the past six years.

Jharkhand police, assisted by paramilitary forces, scourged Naxal-infested areas in Ghatsila sub-division and were helped by West Bengal police from across the border looking for the assailants of Mahato.