The high court had earlier ordered a CBI investigation into the killings of the nine people at Bogtui village.
Saifuddin Laskar (47), TMC area president of Bamungachi area in Joynagar was shot dead from close range near his house by miscreants when he went out to offer prayers in the morning, the police said.
The West Bengal police's bomb squad recovered crude bombs recovered near the home of Palash Sheikh, the absconding accused in the Bhadu Sheikh murder case, at Bogtui village, Birbhum district.
In the over 20-page report, the central probe agency has also stated that the seven persons whose charred bodies were recovered from inside one of the burnt houses in Bogtui village, were "assaulted before being burnt alive".
One was nabbed from the West Bengal-Jharkhand boundary in Birbhum, one from Rampurhat and the third from Malda district on Tuesday night, a police officer said.
An air of gloom hangs in the Bogtui village post-arson as most villagers have moved out from their homes and several others are making moves.
Family members of Bhadu Sheikh, the TMC panchayat leader whose killing on Monday is suspected to have sparked off the attack with petrol bombs on some 10 houses in Bogtui village on the outskirts of Rampurhat town, claimed that Sheikh's sons were among those arrested.
The CBI source alleged that the body of the accused was found in the washroom of the office which the agency has set up in a guest house in Rampurhat.
Hours after West Bengal Chief Minister Mamata Banerjee took a tough stance and ordered the hunting down of all suspects of the Birbhum carnage including her party colleagues, the police on Thursday arrested a local Trinamool Congress boss Anarul Hossain from near a hotel in the pilgrimage town of Tarapith.
'We were sleeping when suddenly we heard the sounds of bombs exploding'
These are the first arrests made by the CBI since it took over the probe into the March 21 killings in Bogtui village following the Calcutta high court's order.
Days after the prime accused in the arson and violence in Bengal's Bogtui village was found hanging in a temporary office of the Central Bureau of Investigation (CBI), the probe agency on Wednesday shifted the makeshift set up in Rampurhat to the metropolis, a senior official said.
The seven have been booked on the charge of murder and other sections of the Indian Penal Code, a CID official said.
Eight people -- all women and children -- were beaten and burnt alive by a mob on Tuesday.
The stampede occurred when people rushed towards the dais in an attempt to get blankets.
'I can only say that it was a revenge killing. We have seen everything from inside our houses. We ran into our dwellings on hearing a mob approaching Sonu's house and hurling bombs. After that, I don't know anything'
The meeting was held for over an hour, he said.
Eight persons died in the early hours of Tuesday after their houses caught fire at Rampurhat in Birbhum district, police said.
As soon as the Zero Hour began, several BJP MPs showed placards and raised slogans against the West Bengal government, led by Chief Minister Mamata Banerjee.
The move came after a nine-member delegation of Bharatiya Janata Party MPs from West Bengal met Union Home Minister Amit Shah and sought his intervention and action against the perpetrators of the crime.
His rise has been phenomenal after the party came to power in 2011. He runs the local syndicate which is involved in extortion from local businesses and also involved in illegal mining of sand
The cycle of violence resulting from the increasing criminalisation of politics cannot stop, will not stop, unless there is a wider political consensus against relying on criminal mafias for electoral purposes, argues Virendra Kapoor.